Nonvolatile semiconductor memory device and method for manufacturing same

ABSTRACT

A nonvolatile semiconductor memory device includes: a semiconductor member; a memory film provided on a surface of the semiconductor member and being capable of storing charge; and a plurality of control gate electrodes provided on the memory film, spaced from each other, and arranged along a direction parallel to the surface. Average dielectric constant of a material interposed between one of the control gate electrodes and a portion of the semiconductor member located immediately below the control gate electrode adjacent to the one control gate electrode is lower than average dielectric constant of a material interposed between the one control gate electrode and a portion of the semiconductor member located immediately below the one control gate electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2008-144736, filed on Jun. 2,2008; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a nonvolatile semiconductor memory device anda method for manufacturing the same.

2. Background Art

Conventionally, nonvolatile semiconductor memory devices such as NANDflash memories have been fabricated by two-dimensionally integratingelements on the surface of a silicon substrate. In this type of flashmemory, increasing the degree of integration by downscaling is requiredto reduce cost per bit and increase memory capacity. However,downscaling tends to cause the problem of interference between adjacentmemory cells, which leads to malfunction of memory cells. For example,data once stored in a memory cell may be erased by operation of itsadjacent memory cell.

As a technique for increasing the degree of integration of a memory, forexample, JP-A-2007-266143(Kokai) proposes a technique ofthree-dimensionally stacking memory cells. In the technique disclosed inthis publication, electrode films and dielectric films are alternatelystacked on a silicon substrate to form a stacked body, and a pluralityof through holes are formed in this stacked body by a single processing.A charge storage layer is formed on the side surface of the throughhole, and then silicon is buried inside the through hole to form asilicon pillar. Thus, a memory cell is formed at the intersectionbetween each electrode film and each silicon pillar, resulting in athree-dimensional arrangement of memory cells.

However, even in this type of three-dimensionally stacked memory, theelectrode film and the dielectric film need to be thinned to increasethe number of stacked films for higher degree of integration whilerestricting the aspect ratio of the through hole. Furthermore, thinningthe electrode film and the dielectric film decreases the distancebetween memory cells arranged along the silicon pillar, and again tendsto cause interference between adjacent memory cells.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a nonvolatilesemiconductor memory device including: a semiconductor member; a memoryfilm provided on a surface of the semiconductor member and being capableof storing charge; and a plurality of control gate electrodes providedon the memory film, spaced from each other, and arranged along adirection parallel to the surface, average dielectric constant of amaterial interposed between one of the control gate electrodes and aportion of the semiconductor member located immediately below thecontrol gate electrode adjacent to the one control gate electrode beinglower than average dielectric constant of a material interposed betweenthe one control gate electrode and a portion of the semiconductor memberlocated immediately below the one control gate electrode.

According to another aspect of the invention, there is provided anonvolatile semiconductor memory device including: a semiconductormember; a memory film provided on a surface of the semiconductor memberand being capable of storing charge; and a plurality of control gateelectrodes and intercellular dielectric films provided on the memoryfilm and alternately arranged along a direction parallel to the surface,at least a portion of the intercellular dielectric film protrudes towardthe semiconductor member.

According to still another aspect of the invention, there is provided amethod for manufacturing a nonvolatile semiconductor memory device,including: alternately forming control gate electrodes and intercellulardielectric films on a substrate to form a stacked body; forming athrough hole in the stacked body, the through hole extending in thestacking direction of the control gate electrode and the intercellulardielectric film; removing a portion of the control gate electrodeexposed to a side surface of the through hole; forming a memory filmcapable of storing charge on the side surface of the through hole; andforming a semiconductor member inside the through hole.

According to still another aspect of the invention, there is provided amethod for manufacturing a nonvolatile semiconductor memory device,including: alternately forming control gate electrodes and intercellulardielectric films on a substrate to form a stacked body; forming athrough hole in the stacked body, the through hole extending in thestacking direction of the control gate electrode and the intercellulardielectric film; removing a portion of the intercellular dielectric filmon a side surface of the through hole; forming a memory film capable ofstoring charge on the side surface of the through hole; and forming asemiconductor member inside the through hole, the forming anintercellular dielectric film including: depositing doped silicon oxideto form a lower portion; depositing non-doped silicon oxide to form anintermediate portion; and depositing doped silicon oxide to form anupper portion, and the removing a portion of the intercellulardielectric film being removing a portion of the upper portion and thelower portion exposed to the side surface of the through hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a NAND memory according toa first embodiment of the invention, showing a cross section parallel tothe channel length direction;

FIG. 2 is a cross-sectional view illustrating a NAND memory according toa comparative example of the first embodiment, showing a cross sectionparallel to the channel length direction;

FIG. 3 is a cross-sectional view illustrating a NAND memory according toa first variation of the first embodiment, showing a cross sectionparallel to the channel length direction;

FIG. 4 is a cross-sectional view illustrating a NAND memory according toa second variation of the first embodiment, showing a cross sectionparallel to the channel length direction;

FIGS. 5A to 5C show a NAND memory according to a first example of thefirst embodiment;

FIGS. 6A and 6B are process cross-sectional views illustrating a methodfor manufacturing a NAND memory according to the first example of thefirst embodiment;

FIGS. 7A and 7B are process cross-sectional views illustrating a methodfor manufacturing a NAND memory according to the first example of thefirst embodiment;

FIGS. 8A and 8B are process cross-sectional views illustrating a methodfor manufacturing a NAND memory according to the first example of thefirst embodiment;

FIGS. 9A and 9B show a NAND memory according to a second example of thefirst embodiment;

FIGS. 10A and 10B are process cross-sectional views illustrating amethod for manufacturing a NAND memory according to the second exampleof the first embodiment;

FIGS. 11A and 11B are process cross-sectional views illustrating amethod for manufacturing a NAND memory according to the second exampleof the first embodiment;

FIGS. 12A and 12B are process cross-sectional views illustrating amethod for manufacturing a NAND memory according to the second exampleof the first embodiment;

FIG. 13 is a perspective view illustrating a NAND memory according to athird example of the first embodiment;

FIG. 14 is a cross-sectional view illustrating the NAND memory accordingto the third example of the first embodiment, showing a cross sectionparallel to the stacking direction of control gate electrodes;

FIG. 15 is a cross-sectional view illustrating a NAND memory accordingto a second embodiment of the invention, showing a cross sectionparallel to the channel length direction;

FIG. 16 is a cross-sectional view illustrating a NAND memory accordingto a comparative example of the second embodiment, showing a crosssection parallel to the channel length direction;

FIG. 17 is a cross-sectional view illustrating a NAND memory accordingto a third embodiment, showing a cross section parallel to the channellength direction;

FIG. 18 is a perspective view illustrating a NAND memory according to anexample of the third embodiment;

FIGS. 19A and 19B illustrate the NAND memory according to the example ofthe third embodiment;

FIGS. 20A and 20B are process cross-sectional views illustrating amethod for manufacturing a NAND memory according to the example of thethird embodiment;

FIGS. 21A and 21B are process cross-sectional views illustrating amethod for manufacturing a NAND memory according to the example of thethird embodiment;

FIGS. 22A and 22B are process cross-sectional views illustrating amethod for manufacturing a NAND memory according to the example of thethird embodiment;

FIG. 23 is a cross-sectional view illustrating a NAND memory accordingto a fourth embodiment of the invention, showing a cross sectionparallel to the channel length direction;

FIG. 24 is a cross-sectional view illustrating a NAND memory accordingto a variation of the fourth embodiment, showing a cross sectionparallel to the channel length direction;

FIG. 25 is a cross-sectional view illustrating a NAND memory accordingto an example of the fourth embodiment, showing a cross section parallelto the vertical direction;

FIG. 26 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to the example of the fourthembodiment, showing a cross section parallel to the vertical direction;

FIG. 27 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to the example of the fourthembodiment, showing a cross section parallel to the vertical direction;

FIG. 28 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to the example of the fourthembodiment, showing a cross section parallel to the vertical direction;

FIG. 29 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to the example of the fourthembodiment, showing a cross section parallel to the vertical direction;

FIGS. 30A to 30D are schematic cross-sectional views showing the effectof the example of the fourth embodiment;

FIG. 31 is a cross-sectional view illustrating a NAND memory accordingto an example of the variation of the fourth embodiment, showing a crosssection parallel to the channel length direction;

FIG. 32 is a cross-sectional view illustrating a NAND memory accordingto a fifth embodiment of the invention, showing a cross section parallelto the channel length direction;

FIG. 33 is a cross-sectional view illustrating a NAND memory accordingto a variation of the fifth embodiment, showing a cross section parallelto the channel length direction;

FIG. 34 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to a sixth embodiment of theinvention;

FIG. 35 is a cross-sectional view illustrating a NAND memory accordingto a seventh embodiment of the invention;

FIG. 36 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to the seventh embodiment;

FIG. 37 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to the seventh embodiment;

FIG. 38 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to the seventh embodiment;

FIG. 39 is a cross-sectional view illustrating a NAND memory accordingto a variation of the seventh embodiment;

FIG. 40 is a cross-sectional view illustrating a NAND memory accordingto an eighth embodiment of the invention;

FIG. 41 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to the eighth embodiment;

FIG. 42 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to the eighth embodiment;

FIG. 43 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to the eighth embodiment; and

FIG. 44 is a cross-sectional view illustrating a NAND memory accordingto a variation of the eighth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will now be described with reference to thedrawings.

To begin with, a first embodiment of the invention is described.

The nonvolatile semiconductor memory device according to this embodimentis a NAND memory.

FIG. 1 is a cross-sectional view illustrating the NAND memory accordingto this embodiment, showing a cross section parallel to the channellength direction (bit line direction).

As shown in FIG. 1, the NAND memory 1 according to this embodimentincludes, as a semiconductor member, a semiconductor substrate 11illustratively made of single crystal silicon (Si) having p-typeconductivity. On the surface of this semiconductor substrate 11 isprovided an insulative tunnel dielectric layer 12 illustratively made ofsilicon oxide, and an insulative charge storage layer 13 illustrativelymade of silicon nitride is provided thereon. Furthermore, an insulativecharge block layer 14 illustratively made of alumina is provided on thecharge storage layer 13. The tunnel dielectric layer 12, the chargestorage layer 13, and the charge block layer 14 constitute a memory filmcapable of storing charge.

On the charge block layer 14, control gate electrodes 15 made ofconductor illustratively polycrystalline silicon doped with impuritiesand intercellular dielectric films 16 illustratively made of siliconoxide are alternately and periodically provided along one directionparallel to the surface of the semiconductor substrate 11. That is, theintercellular dielectric film 16 is provided in a spacing region forspacing the control gate electrodes 15 from each other, and thereby thecontrol gate electrodes 15 are spaced and insulated from each other bythe intercellular dielectric film 16. The width of each of the controlgate electrode 15 and the intercellular dielectric film 16 in thisarranging direction is illustratively below 100 nm (nanometers), andmore specifically 50 nm.

A region in the upper portion of the semiconductor substrate 11immediately below the intercellular dielectric film 16 is doped withdopant impurities, such as phosphorus (P), to form an n-type diffusionregion 17. A region in the upper portion of the semiconductor substrate11 immediately below the control gate electrode 15, that is, a regionbetween the diffusion regions 17, serves as a channel region 18. Thatis, in the NAND memory 1, the arranging direction of the control gateelectrodes 15 and the intercellular dielectric films 16 is a channellength direction, and also a bit line direction.

The charge block layer 14 is a continuous film extending in the channellength direction. In the charge block layer 14, the portion 14 aimmediately below the control gate electrode 15 is different incomposition or structure from the portion 14 b immediately below theintercellular dielectric film 16, and the portion 14 b has a lowerdielectric constant than the portion 14 a. It is noted that the portion14 b of the charge block layer 14 is located immediately below thespacing region for spacing the control gate electrodes 15 from eachother.

Several methods exist for making the dielectric constant of the portion14 b lower than the dielectric constant of the portion 14 a, and arebroadly classified into the methods of decreasing the dielectricconstant of the portion 14 b after forming the charge block layer 14,and the methods of increasing the dielectric constant of the portion 14a after forming the charge block layer 14. In the following, specificmethods are illustrated. With regard to the methods described below, itis possible to perform only one of the methods, or more than one of themethods in combination.

The methods of decreasing the dielectric constant of the portion 14 billustratively include the following methods (1)-(5).

(1) Selectively adding hydrogen (H) or a halogen element such aschlorine (Cl) to the portion 14 b.

(2) Selectively adding a noble gas element such as helium (He) or argon(Ar) to the portion 14 b to form micro voids in the portion 14 b.

(3) Selectively adding carbon (C) to the portion 14 b.

(4) Selectively adding to the portion 14 b a metallic element that cancompose a similar compound having a lower dielectric constant than thebase compound constituting the charge block layer 14. The “similarcompound” used herein refers to the compound having elements except theprincipal metallic element in common. For example, in the case where thebase compound of the charge block layer 14 is alumina as describedabove, a low-dielectric metal that can compose a similar compound, i.e.,oxide, having a lower dielectric constant than alumina is added. Forexample, because silicon oxide has a lower dielectric constant thanalumina, silicon is added.

(5) Selectively adding oxygen (O) to the portion 14 b in the case wherethe charge block layer 14 is formed from nitride.

The methods of increasing the dielectric constant of the portion 14 aillustratively include the following methods (6) and (7).

(6) Selectively adding to the portion 14 a a metallic element that cancompose a similar compound having a higher dielectric constant than thebase compound constituting the charge block layer 14. For example, inthe case where the base compound of the charge block layer 14 is aluminaas described above, a high-dielectric metal that can compose, forexample, hafnium oxide or lanthanum oxide having a higher dielectricconstant than alumina, i.e., hafnium (Hf) or lanthanum (La), is added.

(7) Selectively adding nitrogen (N) to the portion 14 a in the casewhere the charge block layer 14 is formed from oxide such as alumina.

The above method (1) makes the concentration of hydrogen or the halogenelement in the portion 14 b higher than the concentration of hydrogen orthe halogen element in the portion 14 a. The above method (2) makes theconcentration of the noble gas element in the portion 14 b higher thanthe concentration of the noble gas element in the portion 14 a. Theabove method (3) makes the carbon concentration in the portion 14 bhigher than the carbon concentration in the portion 14 a. The abovemethod (4) makes the concentration of the low-dielectric metal, such assilicon, in the portion 14 b higher than the concentration of thelow-dielectric metal in the portion 14 a. The above method (5) makes theoxygen concentration in the portion 14 b higher than the oxygenconcentration in the portion 14 a. On the other hand, the above method(6) makes the concentration of the high-dielectric metal in the portion14 a higher than the concentration of the high-dielectric metal in theportion 14 b. The above method (7) makes the nitrogen concentration inthe portion 14 a higher than the nitrogen concentration in the portion14 b.

Thus, in the NAND memory 1, the material (primarily the tunneldielectric layer 12, the charge storage layer 13, and the charge blocklayer 14 b) interposed between one control gate electrode 15 and theportion (channel region 18) of the semiconductor substrate 11immediately below a control gate electrode 15 adjacent to the onecontrol gate electrode 15 has a lower average dielectric constant thanthe material (the tunnel dielectric layer 12, the charge storage layer13, and the charge block layer 14 a) interposed between one control gateelectrode 15 and the portion (channel region 18) of the semiconductorsubstrate 11 immediately below the one control gate electrode 15.

Next, the operation of the NAND memory according to this embodiment isdescribed.

In the NAND memory 1, a field effect-type cell transistor is formed foreach control gate electrode 15, where the tunnel dielectric layer 12,the charge storage layer 13, and the charge block layer 14 b serve as agate dielectric film, and the diffusion region 17 serves as asource/drain region. Furthermore, in the NAND memory 1, a memory stringis formed from a plurality of memory cells connected in series.

By applying a positive electric potential to any one of the control gateelectrodes 15, electrons are injected from the semiconductor substrate11 through the tunnel dielectric layer 12 into the charge storage layer13 (this is referred to as “write operation”). On the other hand, byapplying a negative electric potential to the control gate electrode 15,holes are injected from the semiconductor substrate 11 through thetunnel dielectric layer 12 into the charge storage layer 13, orelectrons stored in the charge storage layer 13 are released to thesemiconductor substrate 11 through the tunnel dielectric layer 12 (thisis referred to as “erase operation”). Thus, a binary data can be writteninto each cell transistor. Furthermore, by discretely controlling thetotal amount of electrons or holes stored in the charge storage layer13, a multilevel data can be written into each cell transistor.Moreover, the amount of electrons or holes stored in the charge storagelayer 13 can be sensed by detecting the threshold of the celltransistor. This enables the written data to be read. Thus, in the NANDmemory 1, a MONOS type (metal-oxide-nitride-oxide-silicon type) memorycell is formed for each control gate electrode 15.

In the NAND memory 1, the portion 14 a of the charge block layer 14having a relatively high dielectric constant is interposed between thecontrol gate electrode 15 and the channel region 18 of the same memorycell (hereinafter also simply referred to as “between the gate and thechannel”), and hence increases the capacitance between the gate and thechannel. Thus, when the potential of the control gate electrode 15 ofthe memory cell to be written (hereinafter referred to as “selectedmemory cell”) is controlled, a strong electrical effect can be exertedon the channel region 18 of this memory cell (hereinafter referred to as“selected channel”).

In contrast, the portion 14 b of the charge block layer 14 having arelatively low dielectric constant is interposed between the controlgate electrode 15 of the selected memory cell and the channel region 18of a memory cell adjacent to this selected memory cell (this channel ishereinafter referred to as “adjacent channel”), and hence decreases thecapacitance between the gate and the adjacent channel. Thus, when thepotential of the control gate electrode of the selected memory cell iscontrolled, the electrical effect exerted on the adjacent channel can bereduced.

Next, the effect of this embodiment is described.

As described above, this embodiment can reduce the electrical effectexerted on the adjacent channel while allowing the control gateelectrode of the selected memory cell to effectively exert electricalcontrol over the selected channel. This serves to reduce the effectwhere the control gate electrode 15 of a memory cell affects thepotential of the channel region 18 of the adjacent memory cell to varythe threshold of the cell transistor constituting this adjacent memorycell (this effect is hereinafter referred to as “neighboring gateeffect”). Consequently, even if the distance between memory celldecreases with the downscaling of the NAND memory cell 1, thisembodiment can prevent interference between memory cells, and avoidmalfunction of memory cells due to threshold variation of the celltransistor.

It is noted that the boundary between the portion 14 a and the portion14 b in the charge block layer 14 does not necessarily need to belocated immediately below the boundary between the control gateelectrode 15 and the intercellular dielectric film 16, but may bedisplaced toward either the control gate electrode 15 or theintercellular dielectric film 16.

To improve the reliability of the memory cell, the boundary between theportion 14 a and the portion 14 b is preferably located on the controlgate electrode 15 side, for the following reason. The charge block layerlocated immediately below the end portion of the control gate electrodehas a degraded film quality due to processing damage during themanufacturing process, and is likely to trap charge. However, decreasingthe dielectric constant of the charge block layer in this region servesto decrease the amount of charge passing through the charge block layerin this region during write/erase operation, thereby reducing the amountof charge traps. The above effect can be achieved by setting the amountof displacement of the boundary to generally 1/10 or more of the widthof the control gate electrode 15.

On the other hand, to accelerate the write/erase operation speed of thememory cell, the boundary between the portion 14 a and the portion 14 bis preferably located on the intercellular dielectric film 16 side, forthe following reason. The electric field between the gate and thechannel in the vicinity of the end portion of the control gate electrodeis relaxed, and this region does not make an effective contribution tothe write/erase operation speed. However, increasing the dielectricconstant of the charge block layer in this region serves to increase theamount of charge passing through the tunnel dielectric layer in thisregion during write/erase operation. The above effect can be achieved bysetting the amount of displacement of the boundary to generally 1/10 ormore of the width of the control gate electrode 15.

The concentration of the element such as chlorine introduced into theportion 14 b of the charge block layer 14 is preferably 1 to 30 atomic %in average concentration. This can decrease the dielectric constant ofthe portion 14 b by approximately 1 to 50%. The average concentrationbeing set to 1 atomic % or more serves to significantly reduce theneighboring gate effect, thereby decreasing the frequency ofmalfunctions of the memory cell. On the other hand, the averageconcentration being set to 30 atomic % or less serves to avoid thedegradation of insulation in the portion 14 b of the charge block layer14, thereby reliably preventing malfunction due to dielectric breakdownfailure or charge leakage.

Next, a comparative example of the first embodiment is described.

FIG. 2 is a cross-sectional view illustrating a NAND memory according tothis comparative example, showing a cross section parallel to thechannel length direction.

As shown in FIG. 2, in the NAND memory C1 according to this comparativeexample, the charge block layer 14 is not divided into portions 14 a and14 b (see FIG. 1), but is entirely uniform in composition and structure.Hence, the dielectric constant is uniform throughout the charge blocklayer 14. For example, the charge block layer 14 is entirely formed fromalumina with no hydrogen or a halogen element introduced therein.

The NAND memory C1 has no particular problem if the distance d2 betweenthe control gate electrode 15 of a memory cell and the channel region 18of a memory cell adjacent thereto is sufficiently larger than thedistance d1 between the control gate electrode 15 and the channel region18 of the same memory cell.

However, if the ratio d2/d1 decreases with the downscaling of the NANDmemory C1, the aforementioned neighboring gate effect occurs. Morespecifically, the potential of the control gate electrode 15 of a memorycell to be written (selected memory cell) affects the potential of thechannel region of a memory cell adjacent to this memory cell (adjacentchannel) to vary the threshold of the cell transistor. This causesmalfunction of the cell transistor. For example, the neighboring gateeffect is not negligible if the ratio d2/d1 is less than 5, and memorymalfunction manifests itself if the ratio d2/d1 is less than 2. Becausethe distance d1 is illustratively 20 to 30 nm, the neighboring gateeffect is not negligible if the spacing between adjacent memory cells isapproximately 100 nm or less. It is noted that the distance d1 canindeed be increased as the dielectric constant of the tunnel dielectriclayer 12, the charge storage layer 13, and the charge block layer 14 isincreased. However, this increases the ratio d2/d1, making theneighboring gate effect more serious.

In contrast, in the above first embodiment, the portion 14 b of thecharge block layer 14 has a lower dielectric constant than the portion14 a. Hence, the electrically effective value of the ratio d2/d1 can bemade larger than its physical value. More specifically, the electricallyeffective value (d2/ε2)/(d1/ε1) can be increased, where ε2 is theaverage dielectric constant between the control gate electrode of theselected memory cell and the adjacent channel, and ε1 is the averagedielectric constant between the control gate electrode of the selectedmemory cell and the selected channel. Thus, interference between memorycells can be prevented despite the downscaling of the NAND memory.

Next, a first variation of the first embodiment is described.

FIG. 3 is a cross-sectional view illustrating a NAND memory according tothis variation, showing a cross section parallel to the channel lengthdirection.

As shown in FIG. 3, in the NAND memory 1 a according to this variation,not only in the charge block layer 14 but also in the charge storagelayer 13 is the dielectric constant different between the portion 13 aimmediately below the control gate electrode 15 and the portion 13 bimmediately below the intercellular dielectric film 16. That is, theportion 13 b has a lower dielectric constant than the portion 13 a. Themethod for making the dielectric constant of the portion 13 b of thecharge storage layer 13 lower than the dielectric constant of theportion 13 a can be based on those similar to the methods for making thedielectric constant of the portion 14 b of the charge block layer 14lower than the dielectric constant of the portion 14 a in the abovefirst embodiment. For example, hydrogen or a halogen element can beselectively added to the portion 13 b of the charge storage layer 13.

According to this variation, the low-dielectric portion (the portion 14b and the portion 13 b) interposed between the selected gate and theadjacent channel is expanded as compared with the above firstembodiment, and hence interference between memory cells can be preventedmore effectively. The configuration, operation, and effect of thisvariation other than the foregoing are the same as those of the abovefirst embodiment.

Also in this variation, as viewed from above, that is, in the directionperpendicular to the upper surface of the semiconductor substrate 11,the boundary between the control gate electrode 15 and the intercellulardielectric film 16, the boundary between the portion 14 a and theportion 14 b in the charge block layer 14, and the boundary between theportion 13 a and the portion 13 b in the charge storage layer 13 do notnecessarily need to be aligned with each other.

Next, a second variation of the first embodiment is described.

FIG. 4 is a cross-sectional view illustrating a NAND memory according tothis variation, showing a cross section parallel to the channel lengthdirection.

As shown in FIG. 4, in the NAND memory 1 b according to this variation,not only in the charge block layer 14 and the charge storage layer 13but also in the tunnel dielectric layer 12 is the dielectric constantdifferent between the portion 12 a immediately below the control gateelectrode 15 and the portion 12 b immediately below the intercellulardielectric film 16, and the portion 12 b has a lower dielectric constantthan the portion 12 a. The method for making the dielectric constant ofthe portion 12 b of the tunnel dielectric layer 12 lower than thedielectric constant of the portion 12 a can be based on those similar tothe methods for making the dielectric constant of the portion 14 b ofthe charge block layer 14 lower than the dielectric constant of theportion 14 a in the above first embodiment.

According to this variation, the low-dielectric portion (portions 14 b,13 b, 12 b) interposed between the selected gate and the adjacentchannel is expanded as compared with the above first embodiment and thefirst variation thereof, and hence interference between memory cells canbe prevented more effectively. The configuration, operation, and effectof this variation other than the foregoing are the same as those of theabove first embodiment.

Also in this variation, as viewed from above, the boundary between thecontrol gate electrode 15 and the intercellular dielectric film 16, theboundary between the portion 14 a and the portion 14 b in the chargeblock layer 14, the boundary between the portion 13 a and the portion 13b in the charge storage layer 13, and the boundary between the portion12 a and the portion 12 b in the tunnel dielectric layer 12 do notnecessarily need to be aligned with each other.

Next, a first example of the first embodiment is described.

FIGS. 5A to 5C show a NAND memory according to this example, where FIG.5A is a cross-sectional view parallel to the channel length direction(bit line direction), FIG. 5B is a cross-sectional view parallel to thechannel width direction (word line direction), and FIG. 5C is aperspective view.

In FIG. 5C, for convenience of illustration, the intercellulardielectric film 114 is not shown.

As shown in FIGS. 5A to 5C, the NAND memory 100 according to thisexample is a horizontal-type flash memory. The NAND memory 100 includesa silicon substrate 101 illustratively made of p-type single crystalsilicon. On the silicon substrate 101, a silicon oxynitride layer 102serving as a tunnel dielectric layer, a silicon nitride layer 103serving as a charge storage layer, and an alumina layer 104 serving as acharge block layer are stacked in this order, and a polycrystallinesilicon layer 105 made of polycrystalline silicon doped with impuritiesis formed thereon.

In the stacked body of the silicon substrate 101, the silicon oxynitridelayer 102, the silicon nitride layer 103, the alumina layer 104, and thepolycrystalline silicon layer 105, from the upper surface side, deviceisolation trenches 107 having a striped configuration extending in thechannel length direction (bit line direction) are periodically formedalong the channel width direction (word line direction), and a siliconoxide film 108 is buried as a device isolation dielectric film in thedevice isolation trench 107. Thus, the upper portion of the siliconsubstrate 101, the silicon oxynitride layer 102, the silicon nitridelayer 103, the alumina layer 104, and the polycrystalline silicon layer105 are divided along the word line direction. Furthermore, thepolycrystalline silicon layer 105 is divided also along the bit linedirection. That is, the polycrystalline silicon layers 105 are arrangedin a matrix configuration as viewed from above.

In the region of the upper portion of the silicon substrate 101 betweenthe device isolation trenches 107, the region between the immediatelyunderlying regions of the polycrystalline silicon layers 105 is dopedwith impurities to form an n-type diffusion region 112. Hence, as viewedfrom above, the diffusion regions 112 are arranged in a matrixconfiguration. In the upper portion of the silicon substrate 101 betweenthe device isolation trenches 107, the region between the diffusionregions 112, that is, the region immediately below the polycrystallinesilicon layer 105, serves as a channel region 113.

A conductive layer 109 extending in the word line direction is formed onthe polycrystalline silicon layers 105 and the silicon oxide film 108 soas to interconnect the regions immediately above the polycrystallinesilicon layers 105. The conductive layer 109 has a two-layer structureincluding a polycrystalline silicon layer (not shown) on the lower sideand a tungsten silicide layer (not shown) on the upper side. Thepolycrystalline silicon layer 105 and the conductive layer 109constitute a control gate electrode 111. Furthermore, a processing maskmaterial 110 made of silicon nitride is provided immediately above theconductive layer 109. Moreover, an intercellular dielectric film 114made of silicon oxide is provided on the entire surface so as to coverthe control gate electrode 111 and the processing mask material 110.

In the NAND memory 100, the upper portion of the silicon substrate 101partitioned by the device isolation trench 107 extends in the bit linedirection, whereas the upper portion of the control gate electrode 111,that is, the conductive layer 109, extends in the word line direction.Thus, they are in a skew position. Furthermore, a memory film composedof the silicon oxynitride layer 102, the silicon nitride layer 103, andthe alumina layer 104 is provided between the silicon substrate 101 andthe control gate electrode 111. Thus, a cell transistor is formed foreach nearest portion between the conductive layer 109 and the upperportion of the silicon substrate 101. As viewed from above, the celltransistors are arranged in a matrix configuration and connected inseries along the bit line direction. Each cell transistor constitutes amemory cell. The silicon substrate 101 serves as a substrate forsupporting the memory film composed of the silicon oxynitride layer 102,the silicon nitride layer 103, the alumina layer 104 as well as thecontrol gate electrode 111 composed of the polycrystalline silicon layer105 and the conductive layer 109.

In the alumina layer 104 (charge block layer), chlorine is added to theportion 104 b immediately below the intercellular dielectric film 114,and not added to the portion 104 a immediately below the polycrystallinesilicon layer 105. That is, the portion 104 b has a higher chlorineconcentration than the portion 104 a. Thus, the portion 104 b has alower dielectric constant than the portion 104 a.

Next, a method for manufacturing a NAND memory according to this exampleis described.

FIGS. 6A, 6B, 7A, 7B, 8A, and 8B are process cross-sectional viewsillustrating the method for manufacturing a NAND memory according tothis example, where FIGS. 6A, 7A, and 8A show a cross section parallelto the channel length direction, and FIGS. 6B, 7B, and 8B show a crosssection parallel to the channel width direction.

First, as shown in FIGS. 6A and 6B, a silicon substrate 101 doped withdesired impurities is prepared. By performing thermal oxidation andthermal nitridation in combination, a silicon oxynitride layer 102having a thickness of e.g. 5 nm is formed on the upper surface of thesilicon substrate 101. The silicon oxynitride layer 102 serves as atunnel dielectric layer of the NAND memory 100 (see FIG. 5).

Next, by CVD (chemical vapor deposition), a silicon nitride layer 103having a thickness of e.g. 5 nm is deposited on the silicon oxynitridelayer 102. The silicon nitride layer 103 serves as a charge storagelayer of the NAND memory 100 (see FIG. 5).

Next, by ALD (atomic layer deposition), an alumina layer 104 having athickness of e.g. 10 nm is deposited on the silicon nitride layer 103.The alumina layer 104 serves as a charge block layer of the NAND memory100 (see FIG. 5).

Next, by CVD, a polycrystalline silicon layer 105 and a processing maskmaterial 106 are deposited in this order on the alumina layer 104. Thepolycrystalline silicon layer 105 is formed from polycrystalline silicondoped with impurities and has a thickness of e.g. 30 nm. Thepolycrystalline silicon layer 105 constitutes a lower portion of thecontrol gate electrode of the NAND memory 100.

Next, a resist mask (not shown) is formed on the processing maskmaterial 106. This resist mask has a striped pattern extending in thechannel length direction. Then, this resist mask is used as a mask toperform RIE (reactive ion etching) to pattern the processing maskmaterial 106. Next, the resist mask is removed, and the processing maskmaterial 106 patterned is used as a mask to perform etching tosuccessively process the polycrystalline silicon layer 105, the aluminalayer 104, the silicon nitride layer 103, and the silicon oxynitridelayer 102, and etch away the upper portion of the exposed siliconsubstrate 101 to a depth of approximately 100 nm. Thus, a plurality ofdevice isolation trenches 107 extending in the bit line direction areformed.

Next, as shown in FIGS. 7A and 7B, by coating and CMP (chemicalmechanical polishing), a silicon oxide film 108 is buried in the deviceisolation trench 107. The silicon oxide film 108 serves as a deviceisolation dielectric film. Subsequently, the processing mask material106 (see FIG. 6) is removed.

Next, by CVD, a polycrystalline silicon layer doped with impurities isdeposited on the entire surface, and a tungsten silicide layer isconsecutively deposited. Thus, a conductive layer 109 having a thicknessof e.g. 50 nm and having a two-layer structure of the polycrystallinesilicon layer and the tungsten silicide layer is formed on thepolycrystalline silicon layer 105 and the silicon oxide film 108. Theconductive layer 109 constitutes an upper portion of the control gateelectrode. Next, silicon nitride is deposited by CVD to form aprocessing mask material 110 made of silicon nitride.

Next, as shown in FIGS. 8A and 8B, a resist mask (not shown) is formedon the processing mask material 110. This resist mask has a stripedpattern extending in the word line direction. Then, this resist mask isused as a mask to perform RIE to pattern the processing mask material110. Next, the resist mask is removed, and the processing mask material110 patterned is used as a mask to perform RIE to successively processthe conductive layer 109 and the polycrystalline silicon layer 105.Thus, control gate electrodes 111 extending in the word line directionand having a width and spacing of e.g. 50 nm are formed, in which thelower portion is made of the polycrystalline silicon layer 105, and theupper portion is made of the conductive layer 109. Here, the surface ofthe alumina layer 104 is exposed to the region between the control gateelectrodes 111.

Next, the processing mask material 110 and the control gate electrodes111 are used as a mask to ion-implant chlorine molecules (Cl₂) so thatchlorine is selectively introduced into the portion 104 b of the aluminalayer 104 exposed to the region between the control gate electrodes 111.The amount of chlorine introduced is approximately 3×10¹⁵ cm⁻² so that,for example, the decrease of dielectric constant of the portion 104 b isapproximately 10%. Furthermore, the acceleration energy of the chlorinemolecular ion is approximately 10 keV so that, for example, the range ofthe chlorine molecular ion is located around the midpoint of thethickness of the alumina layer 104. Subsequently, heating is performedto a temperature of approximately 1000° C. so that chlorine introducedinto the portion 104 b is combined with alumina constituting the portion104 b. Thus, the dielectric constant of the portion 104 b is decreased.

Next, the processing mask material 110 and the control gate electrodes111 are used as a mask to ion-implant dopant impurities into the upperportion of the silicon substrate 101, followed by heat treatment, sothat a diffusion region 112 is formed in the upper portion of thesilicon substrate 101 between the immediately underlying regions of thecontrol gate electrodes 111. Here, the region of the upper portion ofthe silicon substrate 101 between the diffusion regions 112, that is,the region immediately below the control gate electrode 111, serves as achannel region 113.

Next, as shown in FIGS. 5A and 5B, by CVD, silicon oxide is deposited onthe entire surface to form an intercellular dielectric film 114 thatentirely covers the stacked structure of the control gate electrode 111and the processing mask material 110. Subsequently, interconnect layersand the like (not shown) are formed using known techniques. Thus, theNAND memory 100 according to this example is fabricated.

Next, the effect of this example is described.

In the NAND memory 100 according to this example, in the alumina layer104 serving as a charge block layer, the portion 104 b immediately belowthe intercellular dielectric film 114 has a lower dielectric constantthan the portion 104 a immediately below the polycrystalline siliconlayer 105. Thus, by operation similar to that of the above firstembodiment, in the NAND memory 100, the neighboring gate effect isreduced, and interference between memory cells is less likely to occur.Hence, memory malfunction due to threshold variation of the celltransistor is less likely to occur.

Furthermore, in the NAND memory 100 according to this example, thecharge block layer and the charge storage layer are not divided, butformed as continuous layers, between adjacent memory cells. This servesto avoid gouging of the portion of the silicon substrate 101 where thediffusion region 112 is to be formed, as is the case where the chargeblock layer and the charge storage layer are divided by RIE. Thus,memory malfunction due to the short channel effect of the celltransistor can be reliably avoided. In particular, if the charge blocklayer or the charge storage layer is made of a material resistant to dryetching, e.g., a high-dielectric film such as an alumina film, then thisdividing process is likely to etch away the tunnel dielectric film andthe substrate surface, and the problem of substrate gouging becomesnoticeable. However, according to this example, this problem does notoccur.

It is noted that in this example, chlorine molecules are ion-implantedinto the portion 104 b of the alumina layer 104. However, the doseamount and the acceleration energy can be adjusted to ion-implant otherchlorine-containing molecules. Higher molecular weight of the ion ispreferable, because it facilitates controlling ions in a shallow range.Furthermore, higher molecular weight is preferable also because itcauses significant damage to the charge block layer (alumina layer),which has the effect of increasing the combining efficiency duringhigh-temperature heating. If there is no need to control ions in ashallow range, chlorine atoms can be ion-implanted. Alternatively,halogen elements other than chlorine or hydrogen may be ion-implanted.Further alternatively, argon or other noble gas elements or carbon maybe ion-implanted. In particular, noble gas elements are preferable inthat the diffusion thereof does not significantly degrade thecharacteristics of the surrounding dielectric film. Furthermore, in thecase where the charge block layer is made of alumina, it is alsopossible to ion-implant a metal, such as silicon, having a lowerdielectric constant than the metal constituting the base dielectricmaterial.

In this example as illustrated, a halogen element is introduced into theportion 104 b of the alumina layer 104 by ion implantation, but theinvention is not limited thereto. For example, gas-phase diffusion maybe used. Alternatively, during formation of the intercellular dielectricfilm 114, an intercellular dielectric film containing a large amount ofhalogen element may be formed by adding halogen gas to the source gasatmosphere or using a source gas containing a large amount of halogenelement, and then subjected to heat treatment, so that the halogenelement may be solid-phase diffused into the portion 104 b. For example,an intercellular dielectric film 114 containing chlorine atapproximately 10 atomic % can be formed by forming a silicon oxide filmusing a plasma CVD method based on chlorine gas, silane gas, and nitrousoxide gas, or a plasma CVD method based on silicon tetrachloride gas andnitrous oxide gas, and then subjected to heat treatment, so thatchlorine can be introduced into the portion 104 b at a concentration of1 atomic % or more.

Likewise, hydrogen, a noble gas element, or carbon, or a low-dielectricmetallic element can be contained in the intercellular dielectric film114 and introduced into the portion 104 b by solid-phase diffusion. Thisis free from degradation in the film quality of layers constituting thememory film or degradation in the crystallinity of the silicon substrate101, and a memory cell with superior operating characteristics andreliability can be realized.

Instead of solid-phase diffusion of a halogen element or the like fromthe intercellular dielectric film 114 into the portion 104 b, ahigh-dielectric metallic element may be solid-phase diffused from thecontrol gate electrode 111 into the portion 104 a. For example, informing the polycrystalline silicon layer 105 or the conductive layer109 constituting the control gate electrode 111, a control gateelectrode containing a large amount of high-dielectric metal may beformed by adding a gas containing a high-dielectric metallic elementsuch as tantalum (Ta), hafnium (Hf), zirconium (Zr), or lanthanum (La)to the source gas atmosphere, or using a source gas containing ahigh-dielectric metallic element, and then subjected to heat treatment,so that the high-dielectric metallic element contained in the controlgate electrode may be solid-phase diffused into the portion 104 a of thealumina layer 104.

The amount of element introduced in this case is also preferably 1 to 30atomic % in average concentration. This can increase the dielectricconstant of the portion 104 a by a factor of approximately 1.01 to 2.The average concentration of high-dielectric metal in the portion 104 abeing set to 1 atomic % or more serves to increase the dielectricconstant of the portion 104 a interposed between the selected gate andthe selected channel and increase the physical thickness of the aluminalayer 104. This can further increase the ratio of the capacitancebetween the selected gate and the selected channel to the capacitancebetween the selected gate and the adjacent channel, and hence reduce theneighboring gate effect more reliably. On the other hand, the averageconcentration of high-dielectric metal in the portion 104 a being set to30 atomic % or less serves to ensure insulation of the portion 104 a,thereby reliably preventing malfunction due to dielectric breakdownfailure and charge leakage.

The NAND memory according to the first and second variation of the abovefirst embodiment can also be manufactured by a method similar to that ofthis example. In this case, the dose amount and the acceleration energyfor ion implantation of a halogen element can be suitably selected toselectively introduce the halogen element also into the portion 13 b ofthe charge storage layer 13 and the portion 12 b of the tunneldielectric layer 12. Alternatively, a halogen element can be introducedinto the intercellular dielectric film and solid-phase diffused into theportion 14 b, the portion 13 b, and the portion 12 b by suitablyselecting the condition of subsequent heat treatment. Furtheralternatively, a halogen element or the like can be contained in theportion 14 b of the charge block layer 14 and solid-phase diffused intothe portion 13 b of the charge storage layer 13 and the portion 12 b ofthe tunnel dielectric layer 12. Further alternatively, a halogen elementor the like can be contained in the portion 13 b of the charge storagelayer 13 and solid-phase diffused into the portion 14 b of the chargeblock layer 14 and the portion 12 b of the tunnel dielectric layer 12.Thus, the halogen element or the like can be selectively introduced intothe surface of the portion 14 b and the portion 12 b.

Alternatively, a high-dielectric metallic element may be introduced intothe control gate electrode and solid-phase diffused into the portion 14a, the portion 13 a, and the portion 12 a by suitably selecting thecondition of subsequent heat treatment. Further alternatively, ahigh-dielectric metallic element may be contained in the portion 13 a ofthe charge storage layer 13 and solid-phase diffused into the portion 14a of the charge block layer 14 and the portion 12 a of the tunneldielectric layer 12. Thus, a high-dielectric metallic element can beselectively introduced into the surface of the portion 14 a and theportion 12 a. Consequently, in the charge storage layer 13 and thetunnel dielectric layer 12, the dielectric constant of the portionimmediately below the intercellular dielectric film can be made lowerthan the dielectric constant of the portion immediately below thecontrol gate electrode.

Furthermore, the silicon oxynitride layer 102 serving as a tunneldielectric layer, the silicon nitride layer 103 serving as a chargestorage layer, and the alumina layer 104 serving as a charge block layermay be all formed by ALD.

Next, a second example of the first embodiment is described.

FIGS. 9A and 9B show a NAND memory according to this example, where FIG.9A is a cross-sectional view parallel to the channel length direction(bit line direction), and FIG. 9B is a cross-sectional view parallel tothe channel width direction (word line direction).

As shown in FIGS. 9A and 9B, in the NAND memory 120 according to thisexample, the alumina layer 104 is not divided in the bit line directionor in the word line direction, but spread two-dimensionally.Furthermore, the control gate electrode 111 is divided only along thechannel length direction (bit line direction), and each divided portionextends in the channel width direction (word line direction). Thus, incontrast to the above first example (see FIG. 5), the polycrystallinesilicon layers 105 are not arranged in a matrix configuration as viewedfrom above. Even this structure can achieve the same effect as the abovefirst example.

Next, a method for manufacturing a NAND memory according to this exampleis described.

FIGS. 10A, 10B, 11A, 11B, 12A, and 12B are process cross-sectional viewsillustrating the method for manufacturing a NAND memory according tothis example, where FIGS. 10A, 11A, and 12A show a cross sectionparallel to the channel length direction, and FIGS. 10B, 11B, and 12Bshow a cross section parallel to the channel width direction.

First, as shown in FIGS. 10A and 10B, a silicon substrate 101 doped withdesired impurities is prepared. Then, a silicon oxynitride layer 102 isformed on the upper surface of the silicon substrate 101. Next, by CVD,a silicon nitride layer 103 having a thickness of e.g. 5 nm is depositedon the silicon oxynitride layer 102. Next, a processing mask material106 is deposited on the silicon nitride layer 103.

Next, a resist mask (not shown) is formed on the processing maskmaterial 106. This resist mask has a striped pattern extending in thechannel length direction. Then, this resist mask is used as a mask toperform RIE to pattern the processing mask material 106. Next, theresist mask is removed, and the processing mask material 106 patternedis used as a mask to perform etching to successively process the siliconnitride layer 103 and the silicon oxynitride layer 102, and etch awaythe upper portion of the exposed silicon substrate 101 to a depth ofapproximately 100 nm. Thus, a plurality of device isolation trenches 107extending in the bit line direction are formed.

Next, as shown in FIGS. 11A and 11B, by coating and CMP, a silicon oxidefilm 108 is buried in the device isolation trench 107. Subsequently, theprocessing mask material 106 (see FIG. 10) is removed.

Next, by ALD, an alumina layer 104 having a thickness of e.g. 10 nm isdeposited on the silicon nitride layer 103 and the silicon oxide film108. Next, by CVD, a polycrystalline silicon layer doped with impuritiesis deposited on the entire surface to form a control gate electrode 111.Next, silicon nitride is deposited by CVD to form a processing maskmaterial 110 made of silicon nitride.

Next, as shown in FIGS. 12A and 12B, the processing mask material 110 ispatterned into a striped configuration extending in the word linedirection, and used as a mask to perform RIE to process the control gateelectrode 111. Thus, control gate electrodes 111 extending in the wordline direction are formed. Here, the surface of the alumina layer 104 isexposed to the region between the control gate electrodes 111.

Next, the processing mask material 110 and the control gate electrodes111 are used as a mask to ion-implant chlorine molecules (Cl₂) so thatchlorine is selectively introduced into the portion 104 b of the aluminalayer 104 exposed to the region between the control gate electrodes 111.Thus, the dielectric constant of the portion 104 b is decreased.Subsequently, a method similar to that of the above first example isused to form a diffusion region 112 and the like and cover the structurewith an intercellular dielectric film 114. Thus, the NAND memory 120according to this example is fabricated.

Next, a third example of the first embodiment is described.

FIG. 13 is a perspective view illustrating a NAND memory according tothis example.

FIG. 14 is a cross-sectional view illustrating the NAND memory accordingto this example, showing a cross section parallel to the stackingdirection of control gate electrodes.

In FIG. 13, for convenience of illustration, the intercellulardielectric film 114 is not shown.

As shown in FIGS. 13 and 14, the NAND memory 150 according to thisexample is a vertical-type flash memory. In the NAND memory 150, aplurality of intercellular dielectric films 114 and control gateelectrodes 111 are alternately stacked on a substrate (not shown) toconstitute a stacked body 115. A through hole 116 extending in thestacking direction is formed in the stacked body 115 and penetratesthrough the plurality of control gate electrodes 111 and the pluralityof intercellular dielectric films 114 constituting the stacked body 115.On the side surface of the through hole 116, an alumina layer 104serving as a charge block layer, a silicon nitride layer 103 serving asa charge storage layer, and a silicon oxynitride layer 102 serving as atunnel dielectric layer are stacked in this order. Furthermore, in thethrough hole 116 is provided a silicon pillar 117 illustratively made ofpolycrystalline silicon and shaped like a column, such as a cylindricalcolumn, extending in the stacking direction. The silicon oxynitridelayer 102 is in contact with the silicon pillar 117.

In the NAND memory 150, a plurality of cell transistors are formed alongthe stacking direction of the control gate electrodes 111, that is, theextending direction of the silicon pillar 117. Here, the silicon pillar117 serves as a channel region of the cell transistors. Each celltransistor constitutes a memory cell. Thus, the stacking direction ofthe control gate electrodes 111 is the channel length direction. It isnoted that the silicon pillar 117 corresponds to the semiconductorsubstrate 11 in the above first embodiment (see FIG. 1).

In the alumina layer 104, the portion 104 b between the silicon pillar117 and the intercellular dielectric film 114 has a lower dielectricconstant than the portion 104 a between the silicon pillar 117 and thecontrol gate electrode 111. Methods for making the dielectric constantof the portion 104 b of the alumina layer 104 lower than the dielectricconstant of the portion 104 a illustratively include, as described inthe above first example, the method of allowing the intercellulardielectric film 114 to contain a halogen element, which is solid-phasediffused into the portion 104 b by heat treatment, and the method ofallowing the control gate electrode 111 to contain a high-dielectricmetallic element, which is solid-phase diffused into the portion 104 aby heat treatment.

In such solid-phase diffusion, in contrast to the case of using ionimplantation, there is no degradation in the quality of the dielectricfilm due to knock-on of constituent elements of the dielectric filmduring ion implantation, or degradation in the crystallinity of thesubstrate. Thus, it is possible to realize a NAND memory includingmemory cells with favorable operating characteristics and reliability.It is noted that hydrogen, halogen elements other than chlorine, noblegas elements such as argon, or carbon, or low-dielectric metallicelements may be illustratively introduced into the portion 104 b bysolid-phase diffusion.

According to this example, by operation similar to that of the abovefirst embodiment, the neighboring gate effect can be reduced, andinterference between memory cells can be prevented. As described in thefirst to third example, the above first embodiment is applicable to boththe horizontal-type NAND memory and the vertical-type NAND memory. Asdescribed in the first and second example, in the case where thenonvolatile semiconductor memory device according to the firstembodiment is configured as a horizontal-type memory, the semiconductorsubstrate 11 as a semiconductor member is the silicon substrate 101 forsupporting the memory film and the control gate electrode. It is notedthat the silicon substrate 101 is made of a semiconductor only in itsupper portion. On the other hand, as described in the third example, inthe case where the nonvolatile semiconductor memory device according tothe first embodiment is configured as a vertical-type memory, thesemiconductor substrate 11 is the silicon pillar 17. The same alsoapplies to the first and second variation of the above first embodiment,and the embodiments and the variations thereof described below.

Next, a second embodiment of the invention is described.

FIG. 15 is a cross-sectional view illustrating a NAND memory accordingto this embodiment, showing a cross section parallel to the channellength direction.

As shown in FIG. 15, in the NAND memory 2 according to this embodiment,the charge storage layer 13 and the charge block layer 14 are dividedalong the channel length direction (bit line direction) and providedonly immediately below the control gate electrode 15. An intercellulardielectric film 16 enters between the stacked bodies composed of thecharge storage layers 13 and the charge block layers 14 thus divided.

The tunnel dielectric layer 12 is continuously provided along thechannel length direction. However, in the tunnel dielectric layer 12,the portion 12 a immediately below the control gate electrode 15 isdifferent in dielectric constant from the portion 12 b immediately belowthe intercellular dielectric film 16, and the portion 12 b has a lowerdielectric constant than the portion 12 a. The method for making thedielectric constant of the portion 12 b lower than the dielectricconstant of the portion 12 a can be based on those similar to themethods for making the dielectric constant of the portion 14 b of thecharge block layer 14 lower than the dielectric constant of the portion14 a in the above first embodiment.

This embodiment can also effectively prevent interference between memorycells by operation similar to that of the above first embodiment.Furthermore, interference between memory cells can be prevented moreeffectively by selecting materials so that the intercellular dielectricfilm 16 has a lower dielectric constant than the charge storage layer 13and the charge block layer 14.

In this embodiment, because the charge storage layer 13 is divided alongthe channel length direction, the charge stored in the charge storagelayer 13 of one memory cell does not migrate to the charge storage layer13 of the adjacent memory cell. This also serves to prevent interferencebetween memory cells.

In this embodiment, the boundary between the portion 12 a and theportion 12 b in the tunnel dielectric layer 12 does not necessarily needto be located immediately below the boundary between the control gateelectrode 15 and the intercellular dielectric film 16, but may bedisplaced toward either the control gate electrode 15 or theintercellular dielectric film 16. However, the neighboring gate effectcan be reduced more effectively in the case where the boundary isdisplaced toward the control gate electrode 15, that is, the portion 12b has a larger width in the channel length direction than theintercellular dielectric film 16. The configuration, operation, andeffect of this embodiment other than the foregoing are the same as thoseof the above first embodiment.

Next, a comparative example of the second embodiment is described.

FIG. 16 is a cross-sectional view illustrating a NAND memory accordingto this comparative example, showing a cross section parallel to thechannel length direction.

As shown in FIG. 16, in the NAND memory C2 according to this comparativeexample, the tunnel dielectric layer 12 does not include the portion 12a and the portion 12 b (see FIG. 15) having different dielectricconstants, but is entirely uniform in dielectric constant. Thus, if theratio d2/d1 decreases with the downscaling of the NAND memory C2, theneighboring gate effect occurs and causes interference between memorycells.

Next, a third embodiment of the invention is described.

FIG. 17 is a cross-sectional view illustrating a NAND memory accordingto this embodiment, showing a cross section parallel to the channellength direction.

As shown in FIG. 17, the NAND memory 3 according to this embodiment isdifferent from the NAND memory 1 according to the above first embodiment(see FIG. 1) in that the charge block layer 14 does not include theportion 14 a and the portion 14 b (see FIG. 1), but is entirely uniformin composition.

Furthermore, a dielectric layer 19 is provided between the charge blocklayer 14 and the control gate electrode 15. The dielectric layer 19 isnot provided between the charge block layer 14 and the intercellulardielectric film 16. Thus, the lower surface of the control gateelectrode 15 is located more distant from the semiconductor substrate 11by the thickness of the dielectric layer 19 than the lower surface ofthe intercellular dielectric film 16. In other words, the intercellulardielectric film 16 protrudes downward, that is, toward the semiconductorsubstrate 11, relative to the control gate electrode 15. Theintercellular dielectric film 16 enters between the dielectric layers 19and separates the dielectric layers 19 from each other. The material,composition ratio, film density, amount of impurities contained in thefilm and the like are selected so that the dielectric layer 19 has ahigher dielectric constant than the intercellular dielectric film 16.

In this embodiment, in addition to the tunnel dielectric layer 12, thecharge storage layer 13, and the charge block layer 14, the dielectriclayer 19 having a relatively high dielectric constant is interposedbetween the control gate electrode 15 of the selected memory cell andthe selected channel region 18. Hence, the electrical effect of thecontrol gate electrode 15 exerted on the channel region 18 is relativelylarge. On the other hand, in addition to the tunnel dielectric layer 12,the charge storage layer 13, and the charge block layer 14, theintercellular dielectric film 16 having a relatively low dielectricconstant is interposed between the control gate electrode 15 of theselected memory cell and the adjacent channel region 18. Hence, theelectrical effect of the control gate electrode 15 exerted on theadjacent channel region 18 is relatively small. Consequently, theneighboring gate effect can be reduced, and interference between memorycells can be prevented. For example, memory malfunction due to thresholdvoltage variation of the cell transistor can be avoided. Theconfiguration, operation, and effect of this embodiment other than theforegoing are the same as those of the above first embodiment.

Although FIG. 17 illustratively shows nothing between the charge blocklayer 14 and the intercellular dielectric film 16, this embodiment isnot limited thereto. For example, even a dielectric layer having thesame composition as the dielectric layer 19 can be provided between thecharge block layer 14 and the intercellular dielectric film 16 as longas it has a sufficiently smaller thickness than the dielectric layer 19.Also in this case, the same effect as that of this embodiment can beachieved.

Next, an example of the third embodiment is described.

FIG. 18 is a perspective view illustrating a NAND memory according tothis example.

FIGS. 19A and 19B illustrate the NAND memory according to this example,where FIG. 19A is a cross-sectional view parallel to the verticaldirection, and FIG. 19B is a plan view as viewed from above.

In FIG. 18, for convenience of illustration, the intercellulardielectric film 202 (see FIG. 19) is not shown. Furthermore, althoughthe number of silicon films 203 is illustratively two in FIGS. 18 and19, the number of silicon films 203 is arbitrary.

As shown in FIGS. 18, 19A, and 19B, the NAND memory 200 according tothis example is a vertical-type flash memory similar to the thirdexample of the above first embodiment (see FIGS. 13 and 14). In the NANDmemory 200, a multiple-stacked structure 210 is provided on a siliconsubstrate 201. In the multiple-stacked structure 210, a plurality ofsilicon oxide films 202 and silicon films 203 are stacked along thevertical direction, that is, the direction perpendicular to the uppersurface of the silicon substrate 201. The silicon film 203 is formedfrom silicon doped with an impurity element. The silicon oxide film 202serves as an intercellular dielectric film of the NAND memory 200, andthe silicon film 203 serves as a control gate electrode.

A cylindrical through hole 204 extending in the vertical direction, thatis, the stacking direction of the multiple-stacked structure 210, isformed in the multiple-stacked structure 210. The through hole 204penetrates through the multiple-stacked structure 210 and reaches thesilicon substrate 201. The through hole 204 has a diameter of e.g. 60nm.

On the side surface of the through hole 204, an alumina layer 206serving as a charge block layer and having a thickness of e.g. 10 nm, asilicon nitride layer 207 serving as a charge storage layer and having athickness of e.g. 5 nm, and a silicon oxide layer 208 serving as atunnel dielectric layer and having a thickness of e.g. 5 nm are stackedin this order. Furthermore, inside the through hole 204 is buried asilicon pillar 209 illustratively made of polycrystalline silicon dopedwith impurities and shaped like a cylindrical column.

Furthermore, a silicon nitride layer 205 is formed between the aluminalayer 206 and the silicon film 203. The silicon nitride layer 205corresponds to the dielectric layer 19 in the above third embodiment(see FIG. 17). The silicon nitride layer 205 has a thickness of e.g. 2nm. On the other hand, the silicon nitride layer 205 is not formedbetween the alumina layer 206 and the silicon oxide film 202. Hence, asviewed from the silicon pillar 209, the silicon film 203 is located moredistant than the silicon oxide film 202 by the thickness of the siliconnitride layer 205. Furthermore, the silicon nitride layer 205 has ahigher dielectric constant than the silicon oxide film 202 serving as anintercellular dielectric film. It is noted that the silicon nitridelayer 205 is formed also between the silicon substrate 201 and thealumina layer 206.

Next, a method for manufacturing a NAND memory according to this exampleis described.

FIGS. 20A, 20B, 21A, 21B, 22A, and 22B are process cross-sectional viewsillustrating the method for manufacturing a NAND memory according tothis example, where FIGS. 20A, 21A, and 22A are cross-sectional viewsparallel to the vertical direction, and FIGS. 20B, 21B, and 22B are planviews as viewed from above.

First, as shown in FIGS. 20A and 20B, a silicon substrate 201 isprepared. Then, on the silicon substrate 201, silicon oxide films 202serving as intercellular dielectric films and silicon films 203 servingas control gate electrodes are alternately deposited by CVD to form amultiple-stacked structure 210. Here, the silicon film 203 isillustratively formed from polycrystalline silicon doped withimpurities. Each of the silicon oxide film 202 and the silicon film 203has a thickness of e.g. 50 nm.

Next, as shown in FIGS. 21A and 21B, a resist mask (not shown) is formedon the multiple-stacked structure 210. Next, this resist mask is used asa mask to perform RIE to selectively etch away the multiple-stackedstructure 210 so that the upper surface of the silicon substrate 201 isexposed. Thus, a cylindrical through hole 204 extending in the verticaldirection, reaching the silicon substrate 201, and having a diameter ofe.g. 60 nm is formed in the multiple-stacked structure 210.

Next, thermal nitridation is performed in an ammonia gas atmosphere ornitric monoxide gas atmosphere. Thus, the exposed portion of the siliconfilms 203 and the silicon substrate 201 is selectively nitridized toform a silicon nitride layer 205 having a thickness of e.g. 2 nm. Thus,as viewed from inside the through hole 204, the side surface of thesilicon film 203 is set back from the side surface of the silicon oxidefilm 202 by the thickness of the silicon nitride layer 205.

Next, as shown in FIGS. 22A and 22B, by ALD, on the inner surface of thethrough hole 204, an alumina layer 206 having a thickness of e.g. 10 nm,a silicon nitride layer 207 having a thickness of e.g. 5 nm, and asilicon oxide layer 208 having a thickness of e.g. 5 nm are formed inthis order. As described above, the alumina layer 206 serves as a chargeblock layer, the silicon nitride layer 207 serves as a charge storagelayer, and the silicon oxide layer 208 serves as a tunnel dielectriclayer.

Next, as shown in FIGS. 19A and 19B, a resist mask (not shown) is formedon the multiple-stacked structure 210 and on the inner surface of thethrough hole 204, and used as a mask to perform RIE. Thus, the siliconoxide layer 208, the silicon nitride layer 207, the alumina layer 206,and the silicon nitride layer 205 are selectively removed from thecenter portion of the bottom of the through hole 204 to expose thesurface of the silicon substrate 201.

Subsequently, by CVD, silicon doped with impurities is deposited andburied inside the through hole 204. Next, CMP is performed to removesilicon from the surface of the multiple-stacked structure 210. Thus, asilicon pillar 209 shaped like a cylindrical column is formed inside thethrough hole 204. Thus, the vertical-type NAND memory 200 according tothis example is manufactured.

In the NAND memory 200 according to this example, a plurality of memorycells are arranged along the silicon pillar 209. Furthermore, thesilicon nitride layer 205 is selectively formed between the aluminalayer 206 and the silicon film 203. Thus, by operation similar to thatof the above third embodiment, the neighboring gate effect is reduced,and interference between memory cells is prevented.

In this example as illustrated, the silicon oxide film 202 serving as anintercellular dielectric film is formed by CVD, but it may be formed byother film formation methods, and any other dielectric materialsprimarily composed of silicon and oxygen may be used. Furthermore, thesilicon film 203 serving as a control gate electrode is illustrativelyformed by CVD, but it may be formed by other film formation methods, andany other conductive materials primarily composed of silicon may beused.

In this example as illustrated, thermal nitridation is performed in anammonia gas atmosphere or nitric monoxide gas atmosphere to nitridizethe exposed surface of the silicon film 203, thereby forming the siliconnitride layer 205. However, the method for forming a silicon nitridelayer is not limited thereto. For example, other nitridizing gas may beused, and radical nitridation may be used. Furthermore, instead offorming a silicon nitride layer 205, it is also possible to form asilicon oxide layer by thermal oxidation or radical oxidation. A siliconoxide layer formed by thermal oxidation or radical oxidation has a moredense structure and a higher dielectric constant than the silicon oxidefilm 202 formed by CVD.

Next, a fourth embodiment of the invention is described.

FIG. 23 is a cross-sectional view illustrating a NAND memory accordingto this embodiment, showing a cross section parallel to the channellength direction.

As shown in FIG. 23, the NAND memory 4 according to this embodiment is aMONOS type memory. The NAND memory 4 includes, as a semiconductormember, a semiconductor layer 11 a illustratively made of p-type siliconlike the above first embodiment (see FIG. 1). On the semiconductor layer11 a, a tunnel dielectric layer 12 illustratively made of silicon oxide,a charge storage layer 13 illustratively made of silicon nitride, and acharge block layer 14 illustratively made of alumina are stacked in thisorder. On the charge block layer 14, control gate electrodes 15 made ofconductor illustratively polycrystalline silicon doped with impuritiesand intercellular dielectric films 16 illustratively made of siliconoxide are alternately arranged along the channel length direction. Thewidth of each of the control gate electrode 15 and the intercellulardielectric film 16 in the channel length direction is illustratively 50nm. Furthermore, a diffusion region 17 is formed in the semiconductorlayer 11 a immediately below the intercellular dielectric film 16, andthe region between the diffusion regions 17 serves a channel region 18.

In the NAND memory 4, the intercellular dielectric film 16 protrudestoward the semiconductor layer 11 a relative to the control gateelectrode 15. Thus, the lower surface of the structure composed of theplurality of control gate electrodes 15 and intercellular dielectricfilms 16 is not flat, but forms a corrugated surface with recesses 20formed immediately below the control gate electrodes 15. The memory filmcomposed of the tunnel dielectric layer 12, the charge storage layer 13,and the charge block layer 14 is curved along this corrugated surface.Thus, the tunnel dielectric layer 12, the charge storage layer 13, andthe charge block layer 14 immediately below the control gate electrode15 enter the recess 20. Furthermore, the upper surface of thesemiconductor layer 11 a is also corrugated along this corrugatedsurface, and a projection 11 b is formed in the semiconductor layer 11 aimmediately below the control gate electrode 15. Moreover, thedielectric constant of the intercellular dielectric film 16 in at leastthe protrusion thereof is lower than the average dielectric constant ofthe memory film composed of the tunnel dielectric layer 12, the chargestorage layer 13, and the charge block layer 14, and illustrativelylower than the dielectric constant of any of the tunnel dielectric layer12, the charge storage layer 13, and the charge block layer 14.

Next, the operation and effect of this embodiment are described.

In the NAND memory 4 according to this embodiment, only the tunneldielectric layer 12, the charge storage layer 13, and the charge blocklayer 14 are interposed between the control gate electrode 15 of theselected memory cell and the selected channel region 18. On the otherhand, in addition to the tunnel dielectric layer 12, the charge storagelayer 13, and the charge block layer 14, the intercellular dielectricfilm 16 is also interposed between the control gate electrode 15 of theselected memory cell and the adjacent channel region 18. Hence, ascompared with the distance between the control gate electrode 15 of theselected memory cell and the selected channel region 18 (the distancebetween the selected gate and the selected channel), the distancebetween the selected gate and the adjacent channel is larger.Furthermore, the material interposed between the control gate electrode15 of the selected memory cell and the adjacent channel region 18 has alower average dielectric constant than the material interposed betweenthe control gate electrode 15 of the selected memory cell and theselected channel region 18.

Consequently, while the control gate electrode 15 of a memory cell to bewritten (selected memory cell) is allowed to exert strong electricalcontrol over the channel region 18 of this memory cell (selectedchannel), the electrical effect of the control gate electrode of theselected memory cell exerted on the channel region 18 of the adjacentmemory cell (adjacent channel) can be reduced. This serves to reduce theneighboring gate effect, prevent interference between memory cells, andavoid memory malfunction due to threshold voltage variation of the celltransistor.

Furthermore, in this embodiment, the memory film composed of the tunneldielectric layer 12, the charge storage layer 13, and the charge blocklayer 14 is curved along the corrugated lower surface of the controlgate electrodes 15 and the intercellular dielectric films 16 and enterthe recesses 20. Hence, the effective distance between adjacent memorycells is long in the charge storage layer 13. This can prevent thecharge stored in a memory cell from migrating to the adjacent memorycell.

Furthermore, the charge stored in one memory cell is subjected to aforce counteracting its migration to the adjacent memory cell. This alsoserves to restrict charge migration. More specifically, suppose that ina first memory cell, a positive write potential is applied to thecontrol gate electrode 15 to inject electrons into the charge storagelayer 13, and then a write potential is applied to the control gateelectrode 15 of a second memory cell adjacent to the first memory cell.In this case, the electrons stored in the charge storage layer 13 of thefirst memory cell are subjected to an electrostatic force directed tothe control gate electrode 15 of the second memory cell, that is,directed obliquely upward in FIG. 23. However, for this electron tomigrate from the first memory cell to the second memory cell, it needsto go downward once to circumvent the intercellular dielectric film 16.Thus, the electrons stored in the charge storage layer 13 of the firstmemory cell are subjected to an electrostatic force counteracting itsmigration to the second memory cell, that is, a force directed back tothe first memory cell. Hence, the electrons stored in the first memorycell and being about to diffuse by the self-field, for example, arereturned to the first memory cell by applying a write potential to thesecond memory cell. Consequently, stable charge retentioncharacteristics can be realized.

The NAND memory 4 according to this embodiment may be a horizontal-typenonvolatile memory or vertical-type nonvolatile memory. In the casewhere the NAND memory 4 is a horizontal-type memory, the semiconductorlayer 11 a is illustratively made of a semiconductor substrate formed bydicing a silicon wafer or the like. On the other hand, in the case wherethe NAND memory 4 is a vertical-type memory, the semiconductor layer 11a is illustratively the aforementioned silicon pillar. The same alsoapplies to the variation of this embodiment, and the fifth embodimentand its variation described below.

Next, a variation of the fourth embodiment is described.

FIG. 24 is a cross-sectional view illustrating a NAND memory accordingto this variation, showing a cross section parallel to the channellength direction.

As shown in FIG. 24, the NAND memory 4 a according to this variation isdifferent from the NAND memory 4 according to the above fourthembodiment in that a cavity 21 is formed below the channel region 18 inthe semiconductor layer 11 a. Here, the inside of the cavity 21 may be avacuum or filled with gas.

In this variation, because the cavity 21 is formed, the current flowingthrough the channel region 18 concentrates on the upper portion of thesemiconductor layer 11 a, that is, the portion near the control gateelectrode 15. Thus, by extending the depletion layer from the uppersurface of the semiconductor layer 11 a to the cavity 21, the channelregion 18 can be entirely depleted to turn off the cell transistor,enhancing the electrical control of the control gate electrode of theselected memory cell over the selected channel. This relatively weakensthe electrical effect of the control gate electrode of the selectedmemory cell exerted on the adjacent channel, and the neighboring gateeffect can be further reduced. The configuration, operation, and effectof this variation other than the foregoing are the same as those of theabove fourth embodiment.

The outer edge of the cavity 21 in the channel length direction does notnecessarily need to be located immediately below the boundary betweenthe control gate electrode 15 and the intercellular dielectric film 16,but the aforementioned effect is achieved even if it is displaced towardeither the control gate electrode 15 or the intercellular dielectricfilm 16. Furthermore, the same effect is achieved also by burying adielectric material instead of the cavity 21.

Next, an example of the fourth embodiment is described.

FIG. 25 is a cross-sectional view illustrating a NAND memory accordingto this example, showing a cross section parallel to the verticaldirection.

Although the number of silicon films 203 is illustratively two in FIG.25, the number of silicon films 203 is arbitrary. To increase the degreeof integration of the memory, it is preferable to increase the number ofstacked layers within the allowable range of processing constraints.

As shown in FIG. 25, the NAND memory 300 according to this example is avertical-type flash memory. The NAND memory 300 is different from theNAND memory 200 according to the example of the above third embodiment(see FIGS. 18 and 19) in that, at the side surface of the through hole204, the exposed surface of the silicon film 203 is recessed relative tothe exposed surface of the silicon oxide film 202. Conversely, at theside surface of the through hole 204, the silicon oxide film 202protrudes toward the inside of the through hole 204 relative to thesilicon film 203. In the cross section along the central axis of thethrough hole 204, the protrusion of the silicon oxide film 202illustratively has a rectangular shape. Thus, on the side surface of thethrough hole 204, recesses 211 are periodically formed along thevertical direction to form a corrugated surface. It is noted that theprotrusion of the silicon oxide film 202 may be shaped like a curvedsurface. At the bottom of the through hole 204, a recess 211 a is formedin the silicon substrate 201.

Furthermore, the memory film composed of the alumina layer 206, thesilicon nitride layer 207, and the silicon oxide layer 208 is curvedalong the corrugated side surface of the through hole 204 and entersinside the recesses 211 and 211 a. Moreover, in this example, thesilicon nitride layer 205 is not provided. The configuration of thisexample other than the foregoing is the same as that of the NAND memory200 according to the example of the above third embodiment (see FIGS. 18and 19).

The dimensions of components in the NAND memory 300 are illustrativelyas follows. The silicon oxide film 202 and the silicon film 203 eachhave a thickness of e.g. approximately 50 nm. In the through hole 204,the portion made of the silicon oxide film 202 has a diameter of e.g.approximately 60 nm, and the portion made of the silicon film 203 has adiameter of e.g. approximately 100 nm. That is, at the side surface ofthe through hole 204, the silicon film 203 is set back by approximately20 nm relative to the silicon oxide film 202, and the recess 211 has adepth of 20 nm. Furthermore, the alumina layer 206 serving as a chargeblock layer has a thickness of e.g. approximately 10 nm, the siliconnitride layer 207 serving as a charge storage layer has a thickness ofe.g. approximately 5 nm, and the silicon oxide layer 208 serving as atunnel dielectric layer has a thickness of e.g. approximately 3 nm. Itis noted that a diffusion prevention layer (not shown) illustrativelymade of silicon nitride and having a thickness of e.g. approximately 2nm may be formed outside the alumina layer 206, that is, between thesilicon oxide film 202 and the silicon film 203.

Next, a method for manufacturing a NAND memory according to this exampleis described.

FIGS. 26 to 29 are process cross-sectional views illustrating the methodfor manufacturing a NAND memory according to this example, showing across section parallel to the vertical direction (channel lengthdirection).

First, as shown in FIG. 26, by a method similar to that of the exampleof the above third embodiment (see FIGS. 19 to 22), silicon oxide films202 and silicon films 203 are alternately deposited on a siliconsubstrate 201 to form a multiple-stacked structure 210. The silicon film203 is illustratively formed from polycrystalline silicon doped with animpurity element. Next, as shown in FIG. 27, a through hole 204 isformed in the multiple-stacked structure 210. In a later process, asilicon channel will be formed inside the through hole 204.

Next, as shown in FIG. 28, selective etching is performed on the innersurface of the through hole 204. For example, wet etching is performedusing an etching liquid such as potassium hydroxide solution or diluteaqueous ammonia. Thus, the portion of silicon exposed to the innersurface of the through hole 204 is selectively etched. Consequently, atthe side surface of the through hole 204, the exposed portion of thesilicon film 203 and the silicon substrate 201 is removed, and theexposed surface of the silicon film 203 is set back relative to theexposed surface of the silicon oxide film 202 to form a recess 211.Here, at the bottom of the through hole 204, the silicon substrate 201is etched to form a recess 211 a.

Next, if necessary, a diffusion prevention layer (not shown)illustratively made of silicon nitride having a thickness of 2 nm isformed on the inner surface of the through hole 204. Next, as shown inFIG. 29, by ALD, an alumina layer 206 serving as a charge block layerand having a thickness of e.g. 10 nm, and a silicon nitride layer 207serving as a charge storage layer and having a thickness of e.g. 5 nmare deposited in this order on the inner surface of the through hole204. Next, a silicon oxide layer 208 serving as a tunnel dielectriclayer and having a thickness of e.g. 3 to 5 nm is formed by, forexample, ALD using trisdimethylaminosilane (SiH(N(CH₃)₂)₃, TDMAS) andozone. Thus, a memory film is formed.

Next, as shown in FIG. 25, a resist mask (not shown) is formed on themultiple-stacked structure 210 and on the inner surface of the throughhole 204, and used as a mask to perform RIE. Thus, the silicon oxidelayer 208, the silicon nitride layer 207, and the alumina layer 206 areselectively removed from the center portion of the bottom of the throughhole 204 to expose the surface of the silicon substrate 201.

Subsequently, by selective epitaxial silicon growth, for example,silicon having n-type conductivity is deposited and buried inside thethrough hole 204. Thus, while maintaining the crystallinity of theunderlying silicon substrate 201, silicon can be grown to form a siliconlayer with few crystal defects. Here, silicon is buried also in therecesses 211 and 211 a. Next, CMP is performed to remove silicon fromthe surface of the multiple-stacked structure 210. Thus, a siliconpillar 209 shaped like a cylindrical column is formed inside the throughhole 204. Consequently, the vertical-type NAND memory 300 according tothis example is manufactured.

Next, the operation and effect of this example are described.

FIGS. 30A to 30D are schematic cross-sectional views showing the effectof this example, where FIGS. 30A and 30B show a comparative example inwhich no recesses are formed on the side surface of the through hole,and FIGS. 30C and 30D show this example in which recesses are formed onthe side surface of the through hole.

In the NAND memory 300 according to this example, a plurality of memorycells are arranged along the silicon pillar 209. Furthermore, the recess211 is formed in the portion of the silicon film 203 exposed to theinner surface of the through hole 204. Thus, by operation similar tothat of the above fourth embodiment, the neighboring gate effect can bereduced, and interference between memory cells can be prevented.

More specifically, the silicon oxide film 202 serving as anintercellular dielectric film has a lower dielectric constant than thememory film composed of the alumina layer 206, the silicon nitride layer207, and the silicon oxide layer 208. This serves to reduce theelectrical effect of the potential of one silicon film 203 exerted onthe portion of the silicon pillar 209 surrounded by the adjacent siliconfilm 203, and the neighboring gate effect can be prevented.

Furthermore, preventing charge migration between memory cells alsoserves to prevent interference between memory cells. As shown in FIG.30A, in the NAND memory according to the comparative example in which norecesses are formed on the side surface of the through hole, uponapplication of a positive write potential +Vpgm to the silicon film 203a serving as the control gate electrode of one memory cell, electrons eare stored in the portion of the charge storage layer, that is, thesilicon nitride layer 207, of this memory cell located near the siliconfilm 203 a. However, as shown in FIG. 30B, upon application of the writepotential +Vpgm to the silicon film 203 b of the next memory cell, theelectron e stored near the silicon film 203 a is subjected to anelectrostatic force directed to the silicon film 203 b, and eventuallymigrates toward the silicon film 203 b over time. Furthermore, even ifthe write potential is not applied to the silicon film 203 b, electronsend up migrating by the self-field of the electrons stored. This mayvary the threshold voltage of the cell transistor, and in extreme cases,erase data once written. Such interference between memory cells is morenoticeable as the thickness of the silicon oxide film 202 and thesilicon film 203 decreases, and hence causes a serious problem with thedownscaling of the NAND memory.

In contrast, as shown in FIGS. 30C and 30D, in the NAND memory 300according to this example, at the inner surface of the through hole 204,the silicon oxide film 202 protrudes toward the inside of the throughhole 204. Hence, for the electron e stored in the silicon nitride layer207 near the silicon film 203 a to migrate toward the vicinity of thesilicon film 203 b, it needs to circumvent the protrusion of the siliconoxide film 202, and hence it needs to migrate once toward the inside ofthe through hole 204. However, upon application of the write potential+Vpgm to the silicon film 203 b, an electrostatic force directed to theoutside of the through hole 204 acts on the electrons. This makes itdifficult for the electron e stored in the silicon nitride layer 207near the silicon film 203 a to migrate toward the vicinity of thesilicon film 203 b.

Thus, despite the downscaling of the memory, this example can reduceinterference between memory cells due to migration of electrons. Forexample, this example can prevent data once written in a memory cellfrom being erased when data is written into the adjacent memory cell. Inparticular, in a vertical-type NAND memory like this example, thiseffect is particularly advantageous because in its manufacturingprocess, it is difficult to divide the silicon nitride layer 207 servingas a charge storage layer for each memory cell. The configuration,operation, and effect of this example other than the foregoing are thesame as those of the above fourth embodiment.

In this example as illustrated, the recess 211 is formed by selectiveetching with liquid chemicals. However, other selective etching methodssuch as RIE may be used. Furthermore, in this example as illustrated,the control gate electrode is made of the silicon film 203, but may bemade of a metal film or metal silicide film. In this case, the metalfilm or metal silicide film can be selectively etched by a liquidmixture of aqueous ammonia and hydrogen peroxide solution diluted withwater to form a recess 211.

Next, an example of the variation of the above fourth embodiment isdescribed.

FIG. 31 is a cross-sectional view illustrating a NAND memory accordingto this example, showing a cross section parallel to the verticaldirection (the channel length direction).

As shown in FIG. 31, in the NAND memory 350 according to this example,cavities 212 are formed in the region on the central axis of the siliconpillar 209 surrounded by the silicon film 203 serving as a control gateelectrode. The configuration of the NAND memory 350 other than theforegoing is the same as that of the above NAND memory 300 (FIG. 25).

In this example, when the recess 211 is formed in the step shown in FIG.28 during the process of manufacturing the above NAND memory 300, thewidth and depth of the recess 211 are set to approximately ⅕ or more ofthe diameter of the through hole 204. Furthermore, when the siliconpillar 209 is formed, silicon is deposited by a CVD method with poorstep coverage. Thus, the cavities 212 can be formed in the siliconpillar 209, and the NAND memory 350 according to this example can bemanufactured. The method for manufacturing the NAND memory 350 otherthan the foregoing is the same as the above method for manufacturing theNAND memory 300.

In the NAND memory 350 according to this example, cavities 212 areformed in the silicon pillar 209. Hence, to turn off the celltransistor, the depletion layer only needs to be extended from the outerperipheral surface of the silicon pillar 209 to the cavity 212, and doesnot need to be extended to the center of the silicon pillar 209. Thus,the off-current can be reduced. On the other hand, in the above NANDmemory 300, no cavity is formed in the silicon pillar. Hence, thedepletion layer needs to be extended to the vicinity of the center ofthe silicon pillar 209, which results in decreasing the thresholdvoltage of the cell transistor. However, absence of cavities contributesto increasing the effective cross-sectional area of the silicon pillar209, allowing the on-current to be increased. Whether to form cavitiesin the silicon pillar may be selected in accordance with the requiredcharacteristics of the cell transistor. The operation and effect of thisexample other than the foregoing are the same as those of the abovefourth embodiment and its variation and example.

Next, a fifth embodiment of the invention is described.

FIG. 32 is a cross-sectional view illustrating a NAND memory accordingto this embodiment, showing a cross section parallel to the channellength direction.

As shown in FIG. 32, the NAND memory 5 according to this embodiment is aflash memory of the so-called floating-gate type in which the chargestorage layer is made of a conductor. The NAND memory 5 is differentfrom the NAND memory 4 according to the above fourth embodiment (seeFIG. 23) in that the charge storage layer 53 and the charge block layer14 are divided for each memory cell along the channel length direction,each divided portion of the charge storage layer 53 and the charge blocklayer 14 being housed in the recess 20. Furthermore, the tunneldielectric layer 12 is formed as a continuous film and curved along therecess 20, and the portion of the tunnel dielectric layer 12 immediatelybelow the control gate electrode 15 enters the recess 20. Moreover, thecharge storage layer 53 is made of a conductor, such as a metal. Thus,the divided charge storage layer 53 serves as a floating-gate electrodeof each memory cell, and the cell transistor constituting each memorycell serves as a floating-gate type transistor. The dielectric constantof the intercellular dielectric film 16 is lower than both thedielectric constant of the tunnel dielectric layer 12 and the dielectricconstant of the charge block layer 14. The configuration of thisembodiment other than the foregoing is the same as that of the abovefourth embodiment.

In this embodiment, the tunnel dielectric layer 12, the charge storagelayer 53, and the charge block layer 14 are interposed between thecontrol gate electrode of the selected memory cell and the selectedchannel. On the other hand, the tunnel dielectric layer 12 and theintercellular dielectric film 16 are interposed between the control gateelectrode of the selected memory cell and the adjacent channel. Thus,the average dielectric constant between the control gate electrode ofthe selected memory cell and the adjacent channel is decreased. Thisserves to reduce the neighboring gate effect, prevent interferencebetween memory cells, and avoid memory malfunction due to thresholdvoltage variation of the cell transistor. The operation and effect ofthis embodiment other than the foregoing are the same as those of theabove fourth embodiment.

Next, a variation of the fifth embodiment is described.

FIG. 33 is a cross-sectional view illustrating a NAND memory accordingto this variation, showing a cross section parallel to the channellength direction.

As shown in FIG. 33, in this variation, the variation of the abovefourth embodiment is combined with the fifth embodiment. Morespecifically, in the NAND memory 5 a according to this variation, inaddition to the configuration of the NAND memory 5 according to theabove fifth embodiment (see FIG. 32), a cavity 21 is formed below thecontrol gate electrode 15 in the semiconductor layer 11 a. Theconfiguration of this variation other than the foregoing is the same asthat of the above fifth embodiment. Furthermore, the operation andeffect of this variation other than the foregoing are the same as thosedescribed above in the variation of the fourth embodiment and in thefifth embodiment.

Next, a sixth embodiment of the invention is described.

FIG. 34 is a process cross-sectional view illustrating a method formanufacturing a NAND memory according to this embodiment.

As shown in FIG. 34, the NAND memory 6 according to this embodiment is avertical-type memory. In the process for manufacturing the NAND memory6, a through hole 22 is formed in the stacked body of control gateelectrodes 15 and intercellular dielectric films 16, and the exposedportion of the control gate electrodes is selectively set back. Then, acharge block layer 14 made of alumina and a charge storage layer 13 madeof silicon nitride are formed on the inner surface of the through hole22, followed by anisotropic oxidation by such methods as thermaloxidation or radical oxidation using charged oxidizing species with abias voltage applied to the stacked body (collectively referred to as“bias oxidation”), or oxygen ion implantation. Thus, oxygen isselectively introduced only into the portion 13 c of the charge storagelayer 13 located on the protrusion of the intercellular dielectric film16, and the portion 13 c is selectively oxidized. Consequently, theportion 13 c has a higher oxygen concentration than the portion 13 dformed on the control gate electrode 15.

Consequently, in the silicon nitride constituting the portion 13 c ofthe charge storage layer 13, oxygen (O) is bonded to the dangling bondof silicon (Si) and decreases the density of charge trap states. Thus,in the portion 13 c of the charge storage layer 13, the charge storagecapacity decreases, and the hopping conduction of electrons isrestricted. On the other hand, the portion 13 d of the charge storagelayer 13 formed on the control gate electrode 15 is located in therecess 20. Hence, the portion 13 d is less oxidized, and its chargestorage capacity does not substantially decrease. Consequently, theportion 13 c of the charge storage layer 13 located on the protrusionhas lower charge storage capacity than the portion 13 d formed on thecontrol gate electrode 15. Thus, the portion 13 d having high chargestorage capacity can be divided for each memory cell by the portion 13 chaving low charge storage capacity, and charge migration between memorycells can be prevented. Consequently, interference between memory cellscan be prevented. The configuration, manufacturing method, operation,and effect of this embodiment other than the foregoing are the same asthose of the above fourth embodiment and its example.

In this embodiment as illustrated, oxygen is selectively injected intothe charge storage layer, but the invention is not limited thereto. Anysubstance decreasing the charge storage capacity of the charge storagelayer 13 by addition to the charge storage layer 13 can be injected intothe through hole. For example, it is possible to use any element thatcan be bonded to the dangling bond of the material constituting thecharge storage layer 13 to decrease its density of charge trap states.For example, in the case where the charge storage layer 13 is made ofsilicon nitride, it is possible to inject boron (B), fluorine (F), orchlorine (Cl) besides oxygen. In such cases, the portion 13 c has ahigher concentration of boron, fluorine, or chlorine than the portion 13d.

Next, a seventh embodiment of the invention is described.

FIG. 35 is a cross-sectional view illustrating a NAND memory accordingto this embodiment.

As shown in FIG. 35, the NAND memory 7 according to this embodiment is avertical-type memory. More specifically, the NAND memory 7 includes asemiconductor substrate 11, on which control gate electrodes 15 andintercellular dielectric films 16 are alternately stacked. Furthermore,a through hole 22 extending in the vertical direction, that is, thestacking direction, is formed in the stacked body of the control gateelectrodes 15 and the intercellular dielectric films 16. On the sidesurface of the through hole 22, a diffusion prevention layer 23, acharge block layer 14, a charge storage layer 13, and a tunneldielectric layer 12 are stacked in this order to form a memory film.Furthermore, in the through hole 22, a semiconductor pillar 24 extendingin the vertical direction is provided as a semiconductor member in whicha channel region is to be formed.

Furthermore, in the region of the side surface of the through hole 22located on the intercellular dielectric film 16, a protrusion 25 isformed toward the inside of the through hole 22. The region of the sidesurface of the through hole 22 located between the protrusions 25constitutes a recess 26. In the vertical direction, the protrusion 25corresponds to the center portion of the intercellular dielectric film16. Hence, the vertical width of the protrusion 25 is shorter than thewidth of the intercellular dielectric film 16. On the other hand, in thevertical direction, a control gate electrode 15 is located at the centerportion of the bottom of each recess 26, and the upper and lower end ofthe recess 26 dig into the intercellular dielectric films 16. That is,each recess 26 extends over one control gate electrode 15 and the lowerportion and the upper portion of the intercellular dielectric filmslocated on both sides thereof. Thus, in the vertical direction, that is,the arranging direction of the control gate electrodes 15 and theintercellular dielectric films 16, the bottom of the recess 26 extendsover a region including the control gate electrode 15 and being widerthan the control gate electrode 15. Furthermore, the aforementionedmemory film is corrugated along the corrugated surface formed byalternate arrangement of the protrusions 25 and the recesses 26. Thus,in the vertical direction, the flat region of the charge storage layer13 formed on the recess 26 has a larger width than the control gateelectrode 15.

The dimensions of components are illustratively as follows. The controlgate electrode 15 and the intercellular dielectric film 16 each have athickness of 50 nm. The vertical width of the protrusion 25 is 10 to 30nm. Hence, the recess 26 has a width of 70 to 90 nm. Furthermore, thediffusion prevention layer 23 has a thickness of 2 nm, the charge blocklayer 14 has a thickness of 10 nm, the charge storage layer 13 has athickness of 5 nm, and the tunnel dielectric layer 12 has a thickness of3 nm.

Next, a method for manufacturing a NAND memory according to thisembodiment is described.

FIGS. 36 to 38 are process cross-sectional views illustrating the methodfor manufacturing a NAND memory according to this embodiment.

First, as shown in FIG. 36, intercellular dielectric films 16 andcontrol gate electrodes 15 are alternately formed on a semiconductorsubstrate 11 illustratively made of single crystal silicon. When theintercellular dielectric film 16 is formed, a gas of tetraethoxysilane(TEOS) mixed with trimethoxy borate (TMB) is used as a raw material gasto perform LPCVD (low pressure chemical vapor deposition) to form alower portion 16 a made of silicon oxide doped with impurities, such asboron-doped silicon oxide (BSG, borosilicate glass). Here, the boronconcentration in BSG is illustratively 4 to 5 mass %. Next, a rawmaterial gas containing only TEOS is used to perform LPCVD to form anintermediate portion 16 b made of non-doped silicon oxide. Next, amethod similar to that for forming the lower portion 16 a is used toform an upper portion 16 c made of BSG.

Next, a through hole 22 is formed in the stacked body of the controlgate electrodes 15 and the intercellular dielectric films 16. Then, thecontrol gate electrode 15 is selectively etched away to form a recess 26a in the portion of the control gate electrode 15 exposed to the sidesurface of the through hole 22.

Next, as shown in FIG. 37, the inner surface of the through hole 22 isexposed to a vapor of hydrofluoric acid to selectively etch the lowerportion 16 a and the upper portion 16 c without substantially etchingthe intermediate portion 16 b of the intercellular dielectric film 16.Thus, the portion of the lower portion 16 a and the upper portion 16 cexposed to the inner surface of the through hole 22 is removed, and therecess 26 a (see FIG. 36) is vertically expanded to form a recess 26.Here, instead of dry etching using a vapor of hydrofluoric acid, wetetching using a liquid mixture of hydrofluoric acid and sulfuric acidmay be used.

Next, as shown in FIG. 38, on the inner surface of the through hole 22,a diffusion prevention layer 23, a charge block layer 14, a chargestorage layer 13, and a tunnel dielectric layer 12 are formed in thisorder. Then, these layers are removed from the surface at the bottom ofthe through hole 22. Next, as shown in FIG. 35, silicon is deposited inthe through hole 22 to form a semiconductor pillar 24 extending in thevertical direction. Thus, the NAND memory 7 according to this embodimentis fabricated.

Next, the operation and effect of this embodiment are described.

According to this embodiment, like the above fourth embodiment, theintercellular dielectric film protrudes at the side surface of thethrough hole. Hence, the charge stored in the charge storage layer isdifficult to migrate, achieving superior charge retentioncharacteristics. Consequently, interference between memory cells can beprevented.

Furthermore, according to this embodiment, as compared with the abovefourth embodiment, the recess 26 formed on the side surface of thethrough hole has a larger width. Hence, the portion of the chargestorage layer 13 located near the control gate electrode 15, that is,the portion located at the bottom of the recess 26, has a larger area.Hence, a larger amount of charge is stored in each memory cell, and morefavorable memory characteristics can be achieved.

Furthermore, this embodiment includes a diffusion prevention layer 23,which serves to prevent diffusion of elements between the charge blocklayer 14 and the control gate electrode 15, and between the charge blocklayer 14 and the intercellular dielectric film 16. Thus, it is possibleto reliably avoid insulation degradation in the charge block layer 14,conduction degradation in the control gate electrode 15, and insulationdegradation in the intercellular dielectric film 16.

In this embodiment as illustrated, the lower portion 16 a and the upperportion 16 c of the intercellular dielectric film 16 are formed fromBSG, but this embodiment is not limited thereto. The lower portion 16 aand the upper portion 16 c can be formed from a dielectric materialproviding a sufficient etching selectivity with respect to theintermediate portion 16 b made of non-doped silicon oxide, and canillustratively be formed from silicon oxide doped with impurities.Specifically, instead of BSG, a phosphorus-doped silicon oxide film(PSG, phosphosilicate glass) may be used. For example, in the case ofusing PSG containing phosphorus at 3 to 5 mass %, after the control gateelectrode 15 is selectively etched to form a recess 26 a, dilutehydrofluoric acid treatment can be performed to etch only the lowerportion 16 a and the upper portion 16 c made of PSG withoutsubstantially etching the intermediate portion 16 b.

Furthermore, in this embodiment as illustrated, the diffusion preventionlayer 23 is provided. However, without the diffusion prevention layer23, it is possible to achieve, as described above, the effect ofrestricting charge migration to prevent interference between memorycells and the effect of increasing the amount of charge stored in thememory cell to improve memory characteristics. Furthermore, insulationof the charge block layer 14, conductivity of the control gate electrode15, and insulation of the intercellular dielectric film 16 can bemaintained without problems in practical use. Moreover, also in thisembodiment, like the above sixth embodiment, the charge storage capacityof the portion of the charge storage layer 13 formed on the protrusion25 may be decreased by anisotropic oxidation or the like. This serves tomore effectively restrict charge migration between memory cells and morereliably prevent interference between memory cells.

Next, a variation of the seventh embodiment is described.

FIG. 39 is a cross-sectional view illustrating a NAND memory accordingto this variation.

As shown in FIG. 39, in the NAND memory 7 a according to this variation,a cavity 27 is formed at the center of the semiconductor pillar 24. Thecavity 27 may be filled with a dielectric material. In the above seventhembodiment, when the semiconductor pillar 24 is formed in the throughhole 22, it can be formed by CVD as a thin film on the inner surface ofthe through hole 22. Thus, the space in the through hole 22 enclosed bythe semiconductor pillar 24 constitutes a cavity 27.

According to this variation, when the cell transistor is turned off, thedistance to extend the depletion layer in the semiconductor pillar 24 isdecreased, and hence the cutoff characteristics can be improved. On theother hand, like the above seventh embodiment, if a semiconductormaterial is buried entirely in the through hole 22 to form asemiconductor pillar 24, the on-current can be increased. Theconfiguration, manufacturing method, operation, and effect of thisvariation other than the foregoing are the same as those of the aboveseventh embodiment.

Next, an eighth embodiment of the invention is described.

FIG. 40 is a cross-sectional view illustrating a NAND memory accordingto this embodiment.

As shown in FIG. 40, the NAND memory 8 according to this embodiment is avertical-type memory. The NAND memory 8 is different from the NANDmemory 7 according to the above seventh embodiment (see FIG. 35) in thelayout of recesses formed on the side surface of the through hole 22.

More specifically, in this embodiment, on the side surface of thethrough hole 22, no recess is formed in the region located on thecontrol gate electrode 15, but a recess 28 is formed in each of thevertical end portions of the intercellular dielectric film 16, that is,the lower portion 16 a and the upper portion 16 c. Hence, the recesses28 are spaced from each other by the intermediate portion 16 b of theintercellular dielectric film 16 or the control gate electrode 15. Therecess 28 has a depth of e.g. 20 nm.

Furthermore, in the memory film, the diffusion prevention layer 23, thecharge block layer 14, and the charge storage layer 13 are corrugatedalong the side surface of the through hole 22, whereas the tunneldielectric layer 12 is formed so as to bury the recess 28. Thus, theinterface 29 between the tunnel dielectric layer 12 and thesemiconductor pillar 24 has little step difference, and is nearly flatin the cross section including the central axis of the through hole 22.

Next, a method for manufacturing a NAND memory according to thisembodiment is described.

FIGS. 41 to 43 are process cross-sectional views illustrating the methodfor manufacturing a NAND memory according to this embodiment.

First, as shown in FIG. 41, by a method similar to that of the aboveseventh embodiment, intercellular dielectric films 16 and control gateelectrodes 15 are alternately stacked on a semiconductor substrate 11.Here, when the intercellular dielectric film 16 is formed, a lowerportion 16 a illustratively made of BSG is formed to a thickness of e.g.20 nm, an intermediate portion illustratively made of non-doped siliconoxide is formed to a thickness of e.g. 10 nm, and an upper portion 16 cillustratively made of BSG is formed to a thickness of e.g. 20 nm. Thecontrol gate electrode 15 is illustratively formed from silicon orsilicide. Subsequently, a through hole 22 is formed in the stacked bodyof the intercellular dielectric films 16 and the control gate electrodes15.

Next, as shown in FIG. 42, BSG is selectively etched in an atmosphere ofvapor-phase hydrogen fluoride (HF) to form a recess 28 having a depth ofe.g. approximately 20 nm in the portion of the lower portion 16 a andthe upper portion 16 c exposed to the inner surface of the through hole22.

Next, as shown in FIG. 43, on the inner surface of the through hole 22,a diffusion prevention layer 23, a charge block layer 14, a chargestorage layer 13, and a tunnel dielectric layer 12 are deposited in thisorder to a thickness of e.g. 2 nm, 10 nm, 3 nm, and 5 nm, respectively.Here, the tunnel dielectric layer 12 is formed so that the recess 28 isburied. Next, as shown in FIG. 40, a semiconductor pillar 24 is buriedin the through hole 22. Thus, the NAND memory 8 according to thisembodiment is fabricated.

Next, the operation and effect of this embodiment are described.

Also in this embodiment, for the charge stored in each memory cell tomigrate to the adjacent memory cell, it needs to circumvent theprotrusion made of the intermediate portion 16 b of the intercellulardielectric film 16. Hence, charge migration hardly occurs. Thus,interference between memory cells can be prevented.

Furthermore, no recess is formed in the region of the side surface ofthe through hole 22 located on the control gate electrode 15, but thecharge storage layer 13 is located entirely in the vicinity of thisregion. Hence, a sufficient amount of charge can be stored. Furthermore,the tunnel dielectric layer 12 is buried in the recess 28, and theinterface 29 between the tunnel dielectric layer 12 and thesemiconductor pillar 24 is nearly flat in the cross section parallel tothe vertical direction, that is, the channel length direction. Thus, theouter periphery of the semiconductor pillar 24 serving as a channelregion is flat in the channel length direction along which the currentflows. Hence, the cell transistor is superior in both on-characteristicsand off-characteristics. The configuration, manufacturing method,operation, and effect of this embodiment other than the foregoing arethe same as those of the above seventh embodiment. For example, thediffusion prevention layer 23 may be omitted.

Next, a variation of this embodiment is described.

FIG. 44 is a cross-sectional view illustrating a NAND memory accordingto this variation.

As shown in FIG. 44, in the NAND memory 8 a according to this variation,in addition to the configuration of the NAND memory 8 according to theabove eighth embodiment (see FIG. 40), a cavity 27 is formed at thecenter of the semiconductor pillar 24. The cavity 27 may be filled witha dielectric material.

Like the variation of the above seventh embodiment, this variation canimprove off-characteristics. In particular, in the case where thethrough hole 22 has a sufficiently large diameter, it is possible toachieve favorable off-characteristics while ensuring sufficienton-current. The configuration, manufacturing method, operation, andeffect of this variation other than the foregoing are the same as thoseof the above eighth embodiment.

The above sixth to eighth embodiment and the variations thereof havebeen illustrated with reference to the NAND cell structures of thevertical MONOS type. In this type of vertical NAND memory, theaforementioned effect is particularly advantageous because it isdifficult to separate the charge storage layer for each memory cell.However, applications of these embodiments are not limited tovertical-type NAND memories, but they are also applicable to NANDmemories having the horizontal, that is, planar MONOS cell structure.Also in the horizontal-type NAND memory, charge migration in the chargestorage layer can be prevented by providing a protrusion in theintercellular dielectric film.

The invention has been described with reference to the embodiments andthe variations and examples thereof. However, the invention is notlimited to these embodiments and the like. For example, the aboveembodiments and the variations and examples thereof can be practiced incombination with each other. Furthermore, the materials and dimensionsof components are not limited to those in the above embodiments and thelike. Moreover, those skilled in the art can suitably modify the aboveembodiments and the variations and examples thereof by addition,deletion, or design change of components, or by addition, omission, orcondition change of processes, and such modifications are alsoencompassed within the scope of the invention as long as they fallwithin the spirit of the invention.

1. A nonvolatile semiconductor memory device comprising: a semiconductormember; a memory film provided on a surface of the semiconductor memberand being capable of storing charge; and a plurality of control gateelectrodes provided on the memory film, spaced from each other, andarranged along a direction parallel to the surface, average dielectricconstant of a material interposed between one of the control gateelectrodes and a portion of the semiconductor member located immediatelybelow the control gate electrode adjacent to the one control gateelectrode being lower than average dielectric constant of a materialinterposed between the one control gate electrode and a portion of thesemiconductor member located immediately below the one control gateelectrode.
 2. The memory device according to claim 1, wherein dielectricconstant of a portion of the memory film located immediately below aspacing region spacing the control gate electrodes from each other islower than dielectric constant of a portion of the memory film locatedimmediately below the control gate electrode.
 3. The memory deviceaccording to claim 2, wherein concentration of hydrogen or a halogenelement in the portion of the memory film located immediately below thespacing region is higher than concentration of hydrogen or the halogenelement in the portion of the memory film located immediately below thecontrol gate electrode.
 4. The memory device according to claim 2,wherein concentration of a metallic element composing a similar compoundhaving a lower dielectric constant than base compound of the memory filmis higher in the portion of the memory film located immediately belowthe spacing region than in the portion of the memory film locatedimmediately below the control gate electrode.
 5. The memory deviceaccording to claim 1, further comprising: an intercellular dielectricfilm provided in a spacing region spacing the control gate electrodesfrom each other; and a dielectric layer provided between the memory filmand the control gate electrode and having a higher dielectric constantthan the intercellular dielectric film.
 6. The memory device accordingto claim 1, further comprising: an intercellular dielectric filmprovided in a spacing region spacing the control gate electrodes fromeach other, protruding toward the semiconductor member relative to thecontrol gate electrodes, and having a dielectric constant that is lowerthan average dielectric constant of the memory film, the memory filmentering between the protrusions of the intercellular dielectric film,and a projection toward the control gate electrode being formed in thesemiconductor member immediately below the control gate electrode. 7.The nonvolatile semiconductor memory device according to claim 1,wherein the semiconductor member is a substrate supporting the memoryfilm and the control gate electrode, or an upper portion of thesubstrate.
 8. The memory device according to claim 1, furthercomprising: a substrate, the plurality of control gate electrodes beingstacked on the substrate, the memory film being provided on an innersurface of a through hole penetrating through the plurality of controlgate electrodes, and the semiconductor member being provided inside thethrough hole.
 9. A nonvolatile semiconductor memory device comprising: asemiconductor member; a memory film provided on a surface of thesemiconductor member and being capable of storing charge; and aplurality of control gate electrodes and intercellular dielectric filmsprovided on the memory film and alternately arranged along a directionparallel to the surface, at least a portion of the intercellulardielectric film protrudes toward the semiconductor member.
 10. Thememory device according to claim 9, wherein the protruding portion is acenter portion of the intercellular dielectric film in the arrangingdirection of the control gate electrodes and the intercellulardielectric films.
 11. The memory device according to claim 9, whereinthe protruding portion is both end portions of the intercellulardielectric film in the arranging direction of the control gateelectrodes and the intercellular dielectric films, and the interfacebetween the semiconductor member and the memory film is flat in a crosssection including the arranging direction.
 12. The memory deviceaccording to claim 9, wherein charge storage capacity of a portion ofthe memory film located on the protruding portion is lower than chargestorage capacity of a portion of the memory film located on the controlgate electrode.
 13. The memory device according to claim 12, wherein atleast a layer in the memory film is made of silicon nitride, and oxygenconcentration in the portion of the memory film located on theprotruding portion is higher than oxygen concentration in the portion ofthe memory film located on the control gate electrode.
 14. The memorydevice according to claim 9, wherein a cavity is formed in thesemiconductor member at least immediately below the control gateelectrode.
 15. The memory device according to claim 9, furthercomprising: a substrate, the plurality of control gate electrodes andthe plurality of intercellular dielectric films being stacked on thesubstrate, the memory film being provided on an inner surface of athrough hole penetrating through the plurality of control gateelectrodes and the plurality of intercellular dielectric films, and thesemiconductor member being provided inside the through hole.
 16. Amethod for manufacturing a nonvolatile semiconductor memory device,comprising: alternately forming control gate electrodes andintercellular dielectric films on a substrate to form a stacked body;forming a through hole in the stacked body, the through hole extendingin the stacking direction of the control gate electrodes and theintercellular dielectric films; removing a portion of the control gateelectrode exposed to a side surface of the through hole; forming amemory film capable of storing charge on the side surface of the throughhole; and forming a semiconductor member inside the through hole. 17.The method for manufacturing a memory device according to claim 16,wherein the forming an intercellular dielectric film includes:depositing doped silicon oxide to form a lower portion; depositingnon-doped silicon oxide to form an intermediate portion; and depositingdoped silicon oxide to form an upper portion, and the method furthercomprises: removing a portion of the upper portion and the lower portionof the intercellular dielectric film exposed to the side surface of thethrough hole.
 18. The method for manufacturing a memory device accordingto claim 16, further comprising injecting a substance decreasing chargestorage capacity of the memory film by addition to the memory film intothe through hole.
 19. A method for manufacturing a nonvolatilesemiconductor memory device, comprising: alternately forming controlgate electrodes and intercellular dielectric films on a substrate toform a stacked body; forming a through hole in the stacked body, thethrough hole extending in the stacking direction of the control gateelectrode and the intercellular dielectric film; removing a portion ofthe intercellular dielectric film on a side surface of the through hole;forming a memory film capable of storing charge on the side surface ofthe through hole; and forming a semiconductor member inside the throughhole, the forming an intercellular dielectric film including: depositingdoped silicon oxide to form a lower portion; depositing non-dopedsilicon oxide to form an intermediate portion; and depositing dopedsilicon oxide to form an upper portion, and the removing a portion ofthe intercellular dielectric film being removing a portion of the upperportion and the lower portion exposed to the side surface of the throughhole.
 20. The method for manufacturing a memory device according toclaim 19, wherein the forming a memory film includes: burying the memoryfilm in a recess that is formed in the side surface of the through holeby removal of the exposed portion of the upper portion and the lowerportion.